Filed Pursuant to Rule 424(b)(3)
File Number 333-222200

PROXY STATEMENT FOR SPECIAL MEETING OF STOCKHOLDERS

IBERIABANK CORPORATION

PROSPECTUS

COMMON STOCK

To the Stockholders of Gibraltar Private Bank & Trust Company:

Merger Proposal—Your Vote Is Very Important

You are cordially invited to attend a special meeting of the stockholders of Gibraltar Private Bank & Trust Company (“Gibraltar”) to be held on February 22, 2018 at 10:00 a.m., local time, at 55 Alhambra Plaza, Coral Gables, Florida 33134. At the special meeting, holders of Gibraltar common stock will be asked to consider and vote upon a proposal to adopt and approve an Agreement and Plan of Merger, dated as of October 19, 2017 (the “merger agreement”), entered into by and among Gibraltar, IBERIABANK, a wholly owned subsidiary of IBERIABANK Corporation, and IBERIABANK Corporation, and the merger contemplated by the merger agreement, pursuant to which Gibraltar will merge with and into IBERIABANK (the “merger”). In addition, holders of Gibraltar common stock will be asked to approve the adjournment, postponement, or continuation of the special meeting, if necessary or appropriate, to solicit additional proxies in favor of adoption and approval of the merger and the merger agreement.

If the merger is completed, each outstanding share of Gibraltar common stock will be converted into the right to receive 1.9749 shares of common stock of IBERIABANK Corporation, plus cash in lieu of any fractional share interest of IBERIABANK Corporation common stock. Under the terms of the merger agreement, the exchange ratio may be adjusted in certain circumstances depending on the daily volume weighted average trading prices of IBERIABANK Corporation common stock over a ten day trading period ending on the business day prior to the closing of the merger. However, even with such adjustments to the exchange ratio, the maximum value of the merger consideration to be received by a holder of Gibraltar common stock is $187.3785 per Gibraltar share, and the minimum value is $138.4997 per Gibraltar share (subject to IBERIABANK Corporation’s right to terminate the merger agreement if the measurement price is below $61.88 on the trading day immediately prior to the closing date; See “The Merger Agreement—Termination,” beginning on page 61). Based on the closing prices of IBERIABANK Corporation common stock on the NASDAQ Global Select Market on October 18, 2017 (the last trading day before public announcement of the merger agreement) and January 17, 2018 (the most recent practicable date before the mailing of this proxy statement/prospectus), the value of the merger consideration represented approximately $158.1895 and $163.1267, respectively, for each share of Gibraltar common stock. You should obtain current stock price quotations for IBERIABANK Corporation common stock, which trades on the NASDAQ Global Select Market under the symbol “IBKC.”

Gibraltar’s board of directors has unanimously approved the merger agreement and determined that the merger and the merger agreement are fair to and in the best interests of Gibraltar and its stockholders. Gibraltar’s board of directors unanimously recommends that holders of Gibraltar common stock vote “FOR” the adoption and approval of the merger and the merger agreement and “FOR” the proposal to adjourn the special meeting, if necessary or appropriate, to solicit additional votes in favor of the adoption and approval of the merger and the merger agreement.

The merger cannot be completed unless the proposal to adopt and approve the merger and the merger agreement is approved by the affirmative vote of at least two-thirds of the outstanding shares of Gibraltar common stock.

Your vote is important. Whether or not you plan to attend the special meeting of stockholders, please take the time to vote by either submitting your proxy online or by telephone, or by completing the enclosed proxy card and mailing it in the enclosed envelope as soon as possible to make sure your shares are represented at the special meeting. If you sign, date and mail your proxy card without indicating how you want to vote, your proxy will be counted as a vote “FOR” the adoption and approval of the merger and the merger agreement and “FOR” the proposal to adjourn the special meeting, if necessary or appropriate, to solicit additional votes in favor of the adoption and approval of the merger and the merger agreement. The failure to vote by not submitting your proxy and not attending the special meeting and voting in person will have the same effect as a vote against the adoption and approval of the merger and the merger agreement. Submitting a proxy now will NOT prevent you from being able to vote in person at the special meeting.

The attached proxy statement/prospectus provides you with detailed information about the proposed merger. It also contains or references information about IBERIABANK Corporation and Gibraltar and related matters. You are encouraged to read the proxy statement/prospectus carefully. In particular, you should read the “Risk Factors” section beginning on page 17 for a discussion of the risks you should consider in evaluating the proposed merger and how it may affect you. You can also obtain information about IBERIABANK Corporation from documents that have been filed with the Securities and Exchange Commission that are incorporated in the proxy statement/prospectus by reference.

On behalf of the board of directors, I thank you for your prompt attention to this important matter.

Sincerely yours,

Chairman

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of the securities to be issued in connection with the merger or passed upon the adequacy or accuracy of this proxy statement/prospectus. Any representation to the contrary is a criminal offense.

The securities to be issued in connection with the merger are not savings accounts, deposits or other obligations of any bank or savings association and are not insured by the Federal Deposit Insurance Corporation (which we refer to as the “FDIC”) or any other governmental agency.

This proxy statement/prospectus is dated January 19, 2018, and is first being mailed to Gibraltar’s stockholders on or about January 22, 2018.

GIBRALTAR PRIVATE BANK & TRUST COMPANY

55 Alhambra Plaza, Coral Gables, Florida 33134

NOTICE OF SPECIAL MEETING OF STOCKHOLDERS

TO BE HELD ON FEBRUARY 22, 2018

NOTICE IS HEREBY GIVEN that a special meeting of the holders of common stock of Gibraltar Private Bank & Trust Company (which we refer to as “Gibraltar”) will be held at 55 Alhambra Plaza, Coral Gables, Florida 33134, at 10:00 a.m., local time, on February 22, 2018, for the following purposes:

No other business may be conducted at the special meeting.

Only holders of Gibraltar common stock of record as of the close of business on January 8, 2018 will be entitled to notice of and to vote at the special meeting and any adjournments thereof. The special meeting may be adjourned from time to time upon approval of holders of a majority of the voting shares of Gibraltar represented at the meeting without any notice other than by announcement at the meeting of the adjournment thereof, and any and all business for which notice is hereby given may be transacted at such adjourned meeting.

Your vote is very important. To ensure your representation at the special meeting of stockholders, please submit your proxy online or by telephone, or complete, sign and promptly mail your proxy card in the return envelope enclosed. This will not prevent you from voting in person, but it will help to secure a quorum and avoid added solicitation costs. Your proxy may be revoked at any time before it is voted by following the procedures described in the attached materials.

THE BOARD OF DIRECTORS OF GIBRALTAR UNANIMOUSLY RECOMMENDS THAT YOU VOTE “FOR” THE ADOPTION AND APPROVAL OF THE MERGER PROPOSAL AND “FOR” THE APPROVAL OF THE ADJOURNMENT PROPOSAL.

Holders of Gibraltar common stock have the right to dissent from the merger and obtain payment in cash of the appraised fair value of their Gibraltar shares under applicable statutory provisions and regulations of the Office of the Comptroller of the Currency (“OCC”). In order for a holder of Gibraltar common stock to perfect his or her right to dissent, such holder must carefully follow the procedure set forth in Section 214a(b) of Title 12 of the United States Code. A copy of the applicable statutory and regulatory provisions is included as Appendix C to the accompanying proxy statement/prospectus, and a summary of these provisions can be found under the caption “The Merger—Dissenters’ Rights of Appraisal.”

PLEASE SUBMIT YOUR PROXY ONLINE OR BY TELEPHONE, OR, IF BY MAIL, PLEASE MARK, SIGN, DATE AND RETURN YOUR PROXY CARD PROMPTLY, WHETHER OR NOT YOU PLAN TO ATTEND THE SPECIAL MEETING OF STOCKHOLDERS.

PLEASE DO NOT SEND SHARE CERTIFICATES WITH THE PROXY CARD

ADDITIONAL INFORMATION

The proxy statement/prospectus incorporates important business and financial information about IBERIABANK Corporation from documents that are filed with the Securities and Exchange Commission (which we refer to as the “SEC”) but that are not included in or delivered with the proxy statement/prospectus. You can obtain IBERIABANK Corporation’s documents incorporated by reference in the proxy statement/prospectus without charge by requesting them in writing or by telephone from IBERIABANK Corporation at the following address and telephone number:

IBERIABANK Corporation

200 West Congress Street

Lafayette, Louisiana 70501

Attention: Robert B. Worley, Jr., Secretary

Telephone: (504) 310-7320

To obtain timely delivery of these documents, you must request them no later than five business days before the date of the Gibraltar special meeting. This means that stockholders of Gibraltar requesting documents must do so by February 14, 2018 in order to receive them before the special meeting.

You may also obtain these documents without charge at the SEC’s website (“www.sec.gov”), and you may obtain certain of these documents at IBERIABANK Corporation’s website (“www.iberiabank.com”) by selecting the tab entitled “Investor Relations” and then the tab entitled “SEC Filings.” Other information contained on IBERIABANK Corporation’s website is expressly not incorporated by reference into the proxy statement/prospectus.

The proxy statement/prospectus provides a detailed description of the merger and the merger agreement. We urge you to read the proxy statement/prospectus, including any documents incorporated by reference into the proxy statement/prospectus, and its annexes carefully and in their entirety.

If you have any questions, or need assistance in completing and returning your proxy, you may contact Michael C. Sontag, Corporate Secretary, at the following address and telephone number:

Gibraltar Private Bank & Trust Company

55 Alhambra Plaza

Coral Gables, Florida 33134

Attention: Michael C. Sontag, Corporate Secretary

Telephone: (305) 476-1982

For a more detailed description of the information incorporated by reference in the proxy statement/prospectus and how you may obtain it, see “Where You Can Find More Information,” beginning on page 79.

PLEASE NOTE

Please do not send your stock certificates at this time. You will be sent separate instructions regarding the surrender of your stock certificates.

You should rely only on the information contained in, or incorporated by reference into, the proxy statement/prospectus. No one has been authorized to provide you with information that is different from that contained in, or incorporated by reference into, the proxy statement/prospectus. The proxy statement/prospectus is dated January 19, 2018, and you should assume that the information in the proxy statement/prospectus is accurate only as of such date unless information specifically indicates that another date applies.

The proxy statement/prospectus does not constitute an offer to sell, or a solicitation of an offer to buy, any securities, or the solicitation of a proxy, in any jurisdiction in which or from any person to whom it is unlawful to make any such offer or solicitation in such jurisdiction.

TABLE OF CONTENTS

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QUESTIONS AND ANSWERS ABOUT THE MERGER AND THE SPECIAL MEETING

The following are some questions that you may have regarding the merger and the special meeting, and brief answers to those questions. Gibraltar Private Bank & Trust Company, which we refer to as “Gibraltar,” and IBERIABANK Corporation advise you to read carefully the remainder of this proxy statement/prospectus because the information contained in this section does not provide all of the information that might be important to you with respect to the merger and the special meeting.

For ease of reference, we refer to the merger of Gibraltar with and into IBERIABANK as the “merger.” A copy of the merger agreement is attached to this proxy statement/prospectus as Appendix A.

This document constitutes both a proxy statement of Gibraltar and a prospectus of IBERIABANK Corporation. It is a proxy statement because the board of directors of Gibraltar is using this document to solicit proxies from its stockholders to vote on the adoption and approval of the merger and the merger agreement at a special meeting of stockholders and your proxy will be used at the special meeting or at any adjournment or postponement of the special meeting. It is a prospectus because IBERIABANK Corporation will issue shares of its common stock to Gibraltar stockholders as consideration to be provided in the merger, and this prospectus contains information about that common stock.

This proxy statement/prospectus contains important information about the merger, the merger agreement, the special meeting of Gibraltar’s stockholders and other related matters, and you should read it carefully. The enclosed voting materials for the special meeting allow you to vote your shares of Gibraltar common stock without attending the special meeting in person. Your vote is important, and we encourage you to submit your proxy as soon as possible.

Proposal One: to adopt and approve the merger and the merger agreement, pursuant to which Gibraltar will merge with and into IBERIABANK, a wholly owned subsidiary of IBERIABANK Corporation, with IBERIABANK being the surviving entity following the merger (which we refer to as the “merger proposal”); and

Proposal Two: to approve the adjournment of the Gibraltar special meeting to a later date or dates, if the board of directors of Gibraltar determines it is necessary or appropriate to permit solicitation of additional proxies if there are not sufficient votes at the time of the Gibraltar special meeting to constitute a quorum or to adopt and approve the merger proposal (which we refer to as the “adjournment proposal”).

No other business may be conducted at the special meeting.

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Whether or not you intend to be present at the special meeting, you are urged to submit your proxy online or by telephone, or sign, date and return your proxy card promptly. If you are then present and wish to vote your shares of common stock in person, your original proxy may be revoked by voting at the special meeting.

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RISK FACTORS

In addition to the other information contained in or incorporated by reference into this proxy statement/prospectus, including without limitation, IBERIABANK Corporation’s Annual Report on Form 10-K for the year ended December 31, 2016, and subsequent Quarterly Reports on Form 10-Q, you should carefully consider the following risk factors in deciding whether to vote to adopt and approve the merger proposal.

Risks Associated with the Merger

Fluctuations in the trading price of IBERIABANK Corporation common stock within a certain range will change the value of the shares of IBERIABANK Corporation common stock that you receive in the merger.

If the measurement price of IBERIABANK Corporation common stock is greater than or equal to $70.13 or less than or equal to $94.88 per share, the exchange ratio will equal 1.9749 shares of IBERIABANK Corporation common stock for each share of Gibraltar common stock. Within that range of values, because the number of shares of IBERIABANK Corporation stock you will receive will not change, the value of the shares received will vary with the market price for IBERIABANK Corporation common stock. If the measurement price of IBERIABANK Corporation common stock is higher than this range, then the value of the merger consideration to be received by you in the merger will be a maximum of $187.3785, and if the measurement price is below this range, then the value of the merger consideration to be received by you in the merger will be a minimum of $138.4997, per share of Gibraltar common stock (subject to IBERIABANK Corporation’s right to terminate the merger agreement if the measurement price is below $61.88 on the trading day immediately prior to the closing date; see “The Merger Agreement—Termination,” beginning on page 61).

The market price of IBERIABANK Corporation’s common stock used for the calculation of the measurement price may vary from the price of IBERIABANK Corporation’s common stock on the date the merger agreement was executed, on the date of this proxy statement/prospectus and/or on the date of the Gibraltar special meeting as a result of various factors that are beyond the control of IBERIABANK Corporation and Gibraltar, including but not limited to general market and economic conditions, changes in our respective businesses, operations and prospects, and regulatory considerations. In addition to the adoption and approval of the merger proposal by Gibraltar stockholders, completion of the merger is subject to satisfaction of other conditions that may not occur until after the Gibraltar special meeting. Therefore, at the time of the Gibraltar special meeting you will not know or be able to calculate the precise value of the consideration you will receive at the effective time of the merger. You should obtain current market quotations for shares of IBERIABANK Corporation common stock, which are listed on the NASDAQ Global Select Market under the symbol “IBKC.”

For additional information, see “The Merger Agreement—Conversion of Gibraltar Common Stock,” beginning on page 48.

The market price of IBERIABANK Corporation’s common stock after the merger may be affected by factors different from those affecting the shares of Gibraltar or IBERIABANK Corporation currently.

Upon completion of the merger, holders of Gibraltar common stock will become holders of IBERIABANK Corporation common stock. IBERIABANK Corporation’s business differs from that of Gibraltar, and, accordingly, the results of operations of the combined company and the market price of the combined company’s shares of common stock may be affected by factors different from those currently affecting the results of operations of each of IBERIABANK Corporation and Gibraltar.

The integration of the operations of IBERIABANK and Gibraltar may be more difficult than anticipated.

The success of the merger will depend on a number of factors, including (but not limited to) IBERIABANK and IBERIABANK Corporation’s ability to:

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Acquisitions or mergers entail risks that could negatively affect the operations of IBERIABANK and IBERIABANK Corporation.

Acquisitions and mergers, particularly the integration of companies that have previously been operated separately, involves a number of risks, including, but not limited to:

Any of these risks could result in unexpected losses or expenses and thereby reduce the expected benefits of the acquisition. Also, IBERIABANK Corporation may issue equity securities, including common stock, preferred stock and securities convertible into common stock in connection with future acquisitions, which could cause ownership and economic dilution to the current shareholders of IBERIABANK Corporation (or to the shareholders of IBERIABANK Corporation at that time). Prior to the completion of the pending acquisition, IBERIABANK and Gibraltar have operated and will operate as separate entities. IBERIABANK’s and IBERIABANK Corporation’s failure to successfully integrate these and future acquisitions and/or manage its growth could adversely affect its business, results of operations, financial condition and future prospects.

Holders of Gibraltar common stock will have less influence as shareholders of IBERIABANK Corporation than as stockholders of Gibraltar.

Holders of Gibraltar common stock currently have the right to vote in the election of the board of directors of Gibraltar and on other matters affecting Gibraltar. Based on the number of shares of IBERIABANK Corporation common stock outstanding on January 17, 2018 and the shares expected to be issued in the merger, the stockholders of Gibraltar as a group are expected to own approximately 4.92% of IBERIABANK Corporation’s common stock immediately after the merger. When the merger occurs, each Gibraltar stockholder that receives shares of IBERIABANK Corporation common stock will become a shareholder of IBERIABANK Corporation with a percentage ownership of the combined organization much smaller than such stockholder’s percentage ownership of Gibraltar. Because of this, prior holders of Gibraltar common stock will have less influence on the management and policies of IBERIABANK Corporation than they now have on the management and policies of Gibraltar.

Certain directors and officers of Gibraltar have interests in the merger that may be different from, or in addition to, the interests of non-director or non-management stockholders.

Some of the directors and officers of Gibraltar have interests in the merger that may be different from, or in addition to, the interests of stockholders of Gibraltar generally. These interests exist because of, among other things, existing employment and change in control severance agreements with Gibraltar, ownership of stock options and rights to indemnification and directors and officers insurance for a limited time (at current levels) following the merger. The directors

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of Gibraltar have been invited to join IBERIABANK Corporation’s Miami-Dade Advisory Board following the merger. These interests and arrangements may create potential conflicts of interests. Although the members of each of the IBERIABANK Corporation and Gibraltar board of directors knew about these additional interests and considered them, among other matters, when they approved the merger agreement and the merger, you should be aware of them and understand that some of the directors and officers of Gibraltar will receive payments in connection with the merger that you will not receive.

For a more complete discussion of these interests, see “The Merger—Interests of Certain Gibraltar Directors and Executive Officers in the Merger,” beginning on page 41.

The fairness opinion received by the Gibraltar board of directors from Gibraltar’s financial advisor prior to the signing of the merger agreement does not reflect changes in circumstances since the date of such opinion.

Prior to execution of the merger agreement, the Gibraltar board of directors received a fairness opinion from Gibraltar’s financial advisor, Sandler O’Neill & Partners, L.P. (“Sandler O’Neill”). Gibraltar has not obtained an updated fairness opinion as of the date of this proxy statement/prospectus. Changes in the operations and prospects of Gibraltar or IBERIABANK Corporation, general market and economic conditions and other factors that may be beyond the control of Gibraltar and IBERIABANK Corporation may alter the value of Gibraltar or IBERIABANK Corporation, or the prices of shares of Gibraltar common stock or IBERIABANK Corporation common stock by the time the special meeting takes place or by the time the merger is completed. Sandler O’Neill’s opinion does not speak as of the time the merger will be completed or as of any date other than the date of such opinion. Because Gibraltar does not anticipate asking its financial advisor to update its opinion, the October 16, 2017 opinion does not address the fairness of the merger consideration, from a financial point of view, at the time the merger is completed. The opinion is included as Appendix C to this proxy statement/prospectus.

For a description of the opinion that Gibraltar received from its financial advisor, please refer to “The Merger—Opinion of Gibraltar’s Financial Advisor,” beginning on page 30. For a description of the other factors considered by Gibraltar‘s board of directors in determining to approve the merger, please refer to “The Merger—Gibraltar’s Reasons for the Merger; Recommendation of the Gibraltar Board of Directors,” beginning on page 28.

The merger will not be completed unless important conditions are satisfied.

Specified conditions set forth in the merger agreement must be satisfied or waived to complete the merger. If the conditions are not satisfied or waived, to the extent permitted by law, the merger will not occur or will be delayed and each of IBERIABANK and Gibraltar may lose some or all of the intended benefits of the merger. For a description of these closing conditions, please refer to “The Merger Agreement—Conditions to Complete the Merger,” beginning on page 61.

The merger is subject to the receipt of consents and approvals from governmental entities that may delay the date of completion of the merger or impose conditions that could have an adverse effect on IBERIABANK Corporation.

Before the merger may be completed, various approvals or consents must be obtained from governmental entities. Satisfying the requirements of these governmental entities may delay the date of completion of the merger. In addition, these governmental entities may include conditions to the completion of the merger or require changes to the terms of the merger. While IBERIABANK Corporation and Gibraltar do not currently expect that any such conditions or changes would result in a material adverse effect on IBERIABANK Corporation, there can be no assurance that they will not, and such conditions or changes could have the effect of delaying completion of the merger or imposing additional costs on or limiting the revenues of IBERIABANK Corporation following the merger, any of which might have a material adverse effect on IBERIABANK Corporation following the merger.

Termination of the merger agreement could negatively impact Gibraltar.

If the merger agreement is terminated, there may be various consequences. For example, Gibraltar’s businesses may have been impacted adversely by the failure to pursue other beneficial opportunities due to the focus of its management on the merger, without realizing any of the anticipated benefits of completing the merger. Also, Gibraltar will have incurred substantial expenses in connection with this contemplated transaction without realizing the benefits of the merger. If the merger agreement is terminated and Gibraltar’s board of directors seeks another merger or business combination, Gibraltar’s stockholders cannot be certain that Gibraltar will be able to find a party willing to pay the equivalent or greater consideration

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than that which IBERIABANK Corporation has agreed to pay in the merger. In addition, if the merger agreement is terminated under certain circumstances, including circumstances involving a change in recommendation by Gibraltar’s board of directors, Gibraltar may be required to pay IBERIABANK Corporation a termination fee equal to $9.2 million.

If the merger is not completed, IBERIABANK Corporation and Gibraltar will have incurred substantial expenses without realizing the expected benefits of the merger.

Each of IBERIABANK Corporation and Gibraltar has incurred and will incur substantial expenses in connection with the negotiation and completion of the transactions contemplated by the merger agreement, as well as the costs and expenses of filing, printing and mailing this proxy statement/prospectus and all filing and other fees paid to the SEC in connection with the merger. If the merger is not completed, IBERIABANK Corporation and Gibraltar would have to recognize these expenses without realizing the expected benefits of the merger.

The termination fee and the restrictions on solicitation contained in the merger agreement may discourage other companies from trying to acquire Gibraltar.

The merger agreement contains provisions that make it more difficult for Gibraltar to sell its business to a party other than IBERIABANK Corporation. These provisions include a general prohibition on Gibraltar’s solicitation of any acquisition proposal or offer for a competing transaction, the requirement that Gibraltar pay a termination fee equal to $9.2 million if the merger agreement is terminated in certain circumstances and the requirement that Gibraltar submit the adoption and approval of the merger proposal to a vote of Gibraltar’s stockholders even if Gibraltar’s board of directors changes its recommendation in favor of the adoption and approval of the merger proposal in a manner adverse to IBERIABANK Corporation. For more information, see “The Merger Agreement—Agreement to Not Solicit Other Offers,” “The Merger Agreement—Termination Fee” and “The Merger Agreement—Stockholder Meeting,” beginning on pages 58, 62 and 60, respectively.

These provisions might discourage a third party that might have an interest in acquiring all or a significant part of Gibraltar from considering or proposing that acquisition, even if that party were prepared to pay consideration with a higher per share value than the proposed merger consideration. Furthermore, a potential competing acquiror may propose to pay a lower per share price to Gibraltar’s stockholders than it might otherwise have proposed to pay because of Gibraltar’s obligation, in connection with termination of the merger agreement under certain circumstances, to pay IBERIABANK Corporation a $9.2 million termination fee.

Gibraltar will be subject to business uncertainties and contractual restrictions while the merger is pending.

Uncertainty about the effect of the merger on employees and customers may have an adverse effect on Gibraltar. These uncertainties may impair Gibraltar’s ability to attract, retain and motivate strategic personnel until the merger is consummated, and could cause customers and others that deal with Gibraltar to seek to change existing business relationships with Gibraltar. Experienced employees in the financial services industry are in high demand, and competition for their talents can be intense. Employees of Gibraltar may experience uncertainty about their future roles with the surviving corporation until, or even after, strategies with regard to the combined company are announced or executed. If strategic Gibraltar employees depart because of personal issues relating to the uncertainty and difficulty of integration or a desire not to remain with the surviving entity, Gibraltar’s business following the merger could be harmed. In addition, the merger agreement restricts Gibraltar from making certain acquisitions and taking other specified actions until the merger occurs without the consent of IBERIABANK Corporation. These restrictions may prevent Gibraltar from pursuing attractive business opportunities that may arise prior to the completion of the merger. See “The Merger Agreement—Conduct of Business Pending the Merger,” beginning on page 53.

The shares of IBERIABANK Corporation’s common stock to be received by Gibraltar’s stockholders as a result of the merger will have different rights from shares of Gibraltar common stock.

Following completion of the merger, Gibraltar’s stockholders will become shareholders of IBERIABANK Corporation, and their rights as stockholders will be governed by Louisiana law and IBERIABANK Corporation’s charter and bylaws. There will be important differences between your current rights as a stockholder of Gibraltar and the rights to which you will be entitled as a shareholder of IBERIABANK Corporation. For a discussion of the different rights associated with IBERIABANK Corporation’s common stock and Gibraltar’s common stock, see “Comparison of Stockholder Rights,” beginning on page 67.

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Risks Relating to IBERIABANK Corporation’s Business

You should read and consider risk factors specific to IBERIABANK Corporation’s business that will also affect the combined company after the merger. These risks are described in the sections entitled “Risk Factors” in IBERIABANK Corporation’s Annual Report on Form 10-K for the fiscal year ended December 31, 2016 and in other documents incorporated by reference into this proxy statement/prospectus. For more information, see “Where You Can Find More Information,” beginning on page 79.

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GIBRALTAR PRIVATE BANK & TRUST COMPANY SPECIAL MEETING

Gibraltar is mailing this proxy statement/prospectus to you as a Gibraltar stockholder on or about January 22, 2018. With this proxy statement/prospectus, Gibraltar is sending you a notice of the Gibraltar special meeting of stockholders and a form of proxy that is solicited by the Gibraltar board of directors.

Date, Time and Place of the Special Meeting

The special meeting will be held on February 22, 2018 at 10:00 a.m., local time, at 55 Alhambra Plaza, Coral Gables, Florida 33134.

Matters to be Considered

Holders of Gibraltar common stock will be asked to vote to:

Recommendation of Gibraltar’s Board of Directors

The Gibraltar board of directors has unanimously approved the merger agreement and the transactions contemplated by the merger agreement. The board of directors of Gibraltar has determined that the merger and the merger agreement are fair to Gibraltar stockholders and are in the best interest of Gibraltar and its stockholders and recommends that you vote “FOR” the adoption and approval of the merger proposal. See “The Merger—Gibraltar’s Reasons for the Merger; Recommendation of the Gibraltar Board of Directors,” beginning on page 28.

The Gibraltar board of directors also recommends that holders of common stock vote “FOR” the approval of the adjournment proposal.

Proxy Card, Revocation of Proxy

You should follow the instructions on the proxy card to submit your proxy online or by telephone. If using mail, please promptly complete and return the proxy card accompanying this proxy statement/prospectus to ensure that your vote is counted at the special meeting of stockholders, regardless of whether you plan to attend. You can revoke your proxy at any time before the vote is taken at the special meeting by:

All shares represented by valid proxies received prior to the special meeting and that are not revoked before the vote at the special meeting will be voted in accordance with your instructions on the proxy card. If you sign your proxy card, but make no specification on the card as to how you want your shares voted, your proxy card will be voted, as appropriate, “FOR” adoption and approval of the merger proposal, and “FOR” approval of the adjournment proposal. No other matter may be presented for action at the special meeting.

You should send any notice of revocation or your completed new proxy card, as the case may be, to Gibraltar at the following address:

Gibraltar Private Bank & Trust Company

55 Alhambra Plaza

Coral Gables, Florida 33134

Attention: Corporate Secretary

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If you choose to send a completed proxy card bearing a later date than your original proxy card, the new proxy card must be received before the beginning of the special meeting.

Your vote is important. Whether or not you plan to attend the special meeting, please take the time to vote by submitting your proxy online or by telephone, or by completing and mailing the enclosed proxy card as described on the enclosed instructions as soon as possible to make sure your shares are represented at the special meeting. Submitting your proxy now will NOT prevent you from being able to vote in person at the special meeting.

Voting in Person

If you are a stockholder of record of Gibraltar on January 8, 2018, plan to attend the special meeting and wish to vote in person, you will be given a ballot at the special meeting. If you plan to attend the special meeting, you must hold your shares in your own name or have a letter from the record holder of your shares confirming your ownership. In addition, you must bring a form of personal photo identification with you in order to be admitted to the meeting. Gibraltar reserves the right to refuse admittance to anyone without proper proof of share ownership or without proper photo identification. Whether or not you intend to be present at the special meeting, you are urged to sign, date and return your proxy card or to submit your proxy via the internet or by telephone, promptly. If you are then present and wish to vote your shares in person, your original proxy may be revoked by voting at the special meeting.

Whether or not you plan to attend the special meeting, Gibraltar requests that you complete, sign, date and return the enclosed proxy card as soon as possible in the enclosed postage-paid envelope or submit a proxy through the internet or by telephone as described in the instructions accompanying this proxy statement/prospectus. This will not prevent you from voting in person at the special meeting, but will assure that your vote is counted if you are unable to attend.

Solicitation of Proxies

The enclosed proxy is solicited by and on behalf of Gibraltar’s board of directors. The cost of solicitation of proxies will be borne by Gibraltar. In addition to solicitations by mail, Gibraltar’s directors, officers and regular employees may solicit proxies personally or by telephone. No additional compensation will be paid to directors, officers or other employees of Gibraltar for making these solicitations.

Record Date

The close of business on January 8, 2018 has been fixed as the record date for determining the Gibraltar stockholders entitled to receive notice of and to vote at the special meeting of stockholders. At that time, 1,411,645 shares of Gibraltar common stock were outstanding, and held by approximately 159 holders of record. Each stockholder of record as of that time is entitled to one vote for each share held on each proposal to be considered at the special meeting.

Voting Rights, Quorum Requirement and Vote Required

The presence, in person or by properly executed proxy, of the holders of a majority of the outstanding shares of Gibraltar common stock, is necessary to constitute a quorum at the special meeting of stockholders. All shares of Gibraltar common stock present in person or represented by proxy, including abstentions, will be treated as present and entitled to vote for purposes of determining the presence or absence of a quorum for all matters voted on at the special meeting.

Adoption and approval of the merger proposal requires the affirmative vote of the holders of at least two-thirds of the outstanding shares of Gibraltar common stock. Because the required vote to adopt and approve the merger proposal is based on the number of shares of Gibraltar common stock outstanding, a failure to vote or an abstention will have the same effect as a vote AGAINST the proposal to adopt and approve the merger proposal.

Approval of the adjournment proposal requires a majority of votes cast at the special meeting. A failure to vote or an abstention will not be considered to be a vote that was cast, and will have no effect on this proposal.

Shares Held by Directors and Officers; Voting Agreements

As of the record date, directors and executive officers of Gibraltar had or shared the right to vote 277,735 shares of Gibraltar common stock. This represents approximately 19.67% of the total number of shares of stock entitled to be voted at the special meeting.

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On October 19, 2017, each member of the board of directors of Gibraltar entered into a voting agreement with IBERIABANK Corporation and IBERIABANK, pursuant to which each such director agreed, among other things, to vote the shares of common stock over which they have voting power “FOR” the adoption and approval of the merger agreement, the merger and the other transactions contemplated by the merger agreement, and the other proposals to be considered at the special meeting, subject to certain exceptions. The voting agreements also contain certain restrictions on the transfer of shares of common stock by each such director.

In addition, Gibraltar currently expects that each of its executive officers who are not directors will vote their shares of Gibraltar common stock “FOR” the adoption and approval of the merger proposal even though such persons have not entered into an agreement requiring them to do so.

When considering Gibraltar’s board of directors’ recommendation that you vote in favor of the adoption and approval of the merger proposal, you should be aware that certain of the directors and executive officers of Gibraltar have interests in the merger that may be different from, or in addition to, the interests of Gibraltar’s stockholders generally. For more information, see “The Merger—Interests of Certain Gibraltar Directors and Executive Officers in the Merger,” beginning on page 41.

Stock Certificates

If you are a stockholder of Gibraltar, you should not send in any certificates representing Gibraltar common stock. Following the completion of the merger, you will receive separate instructions for the exchange of your certificates representing Gibraltar common stock.

Assistance

If you need assistance in completing your proxy card, have questions regarding Gibraltar’s special meeting or would like additional copies of this proxy statement/prospectus, please contact Michael C. Sontag, Corporate Secretary, at 55 Alhambra Plaza, Coral Gables, Florida 33134 (Telephone: (305) 476-1982).

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THE MERGER

The description of the merger in this section in this proxy statement/prospectus describes the material information about the merger; however, it does not purport to be complete and may not contain all of the information about the merger that may be important to you. It is qualified in its entirety by reference to the merger agreement, which is attached to this proxy statement/prospectus (without exhibits) as Appendix A hereto and incorporated herein by reference.

General

On October 19, 2017, IBERIABANK Corporation, IBERIABANK and Gibraltar entered into the merger agreement. Pursuant to the merger agreement, Gibraltar will merge with and into IBERIABANK, a wholly owned subsidiary of IBERIABANK Corporation, with IBERIABANK as the surviving entity.

Upon completion of the merger, each share of Gibraltar common stock will be converted into the right to receive 1.9749 shares of IBERIABANK Corporation common stock. This exchange ratio is subject to adjustment depending on the measurement price of IBERIABANK Corporation common stock. If the measurement price is greater than $94.88 per share, each outstanding share of Gibraltar common stock will be converted into the right to receive a number of shares of IBERIABANK Corporation common stock equal to the quotient obtained by dividing $187.3785 by such measurement price. If the measurement price is less than $70.13 per share, each share of Gibraltar common stock will be converted into the right to receive a number of shares of IBERIABANK Corporation common stock equal to the quotient obtained by dividing $138.4997 by the measurement price. Cash will be paid in lieu of any fractional share of IBERIABANK Corporation common stock. See “The Merger Agreement—Conversion of Gibraltar Common Stock,” beginning on page 48.

For additional and more detailed information regarding the legal documents that govern the merger, including information about the conditions to the merger and the provisions for terminating or amending the merger agreement, see “The Merger Agreement,” beginning on page 48.

The board of directors unanimously recommends that holders of Gibraltar common stock vote “FOR” the adoption and approval of the merger proposal.

The Parties to the Merger Agreement

IBERIABANK Corporation and IBERIABANK

IBERIABANK Corporation, a Louisiana corporation, is a financial holding company. IBERIABANK Corporation is the holding company for IBERIABANK, a Louisiana banking corporation headquartered in Lafayette, Louisiana; Lenders Title Company, an Arkansas-chartered title insurance and closing services agency headquartered in Little Rock, Arkansas (“Lenders Title”); IBERIA Capital Partners L.L.C., a corporate finance services firm (“ICP”); 1887 Leasing, LLC, a holding company for our aircraft; IBERIA Asset Management, Inc. (“IAM”), which provides wealth management and trust services to high net worth individuals, pension funds, corporations and trusts; 840 Denning, LLC, which invests in a commercial rental property; and IBERIA CDE, LLC (“CDE”), which invests in purchased tax credits. As of September 30, 2017, IBERIABANK Corporation operated 319 combined offices, including 216 bank branch offices and one loan production office in Louisiana, Arkansas, Tennessee, Alabama, Texas, Florida, South Carolina and Georgia, 24 title insurance offices in Arkansas and Louisiana, and mortgage representatives in 63 locations in 11 states. IBERIABANK Corporation also has fourteen wealth management locations in four states and one IBERIA Capital Partners L.L.C. office in Louisiana. At September 30, 2017, IBERIABANK Corporation had total consolidated assets of $28.0 billion, total unaudited deposits of $21.3 billion and total shareholders’ equity of $3.7 billion.

IBERIABANK offers commercial and retail banking products and services to customers throughout locations in seven states and mortgage banking products in ten states. IBERIABANK provides these products and services in Louisiana, Alabama, Florida, Arkansas, Tennessee, Georgia and Texas. These products and services include a broad array of commercial, consumer, mortgage, and private banking products and services, trust services, cash management, deposit and annuity products. Certain of IBERIABANK Corporation’s non-bank subsidiaries engage in financial services-related activities, including brokerage services, sales of variable annuities, and wealth management services. Lenders Title offers a full line of title insurance and closing services throughout Arkansas and Louisiana. ICP provides equity research, institutional sales and trading, and corporate finance services throughout the energy industry. 1887 Leasing, LLC, owns an aircraft used by management of IBERIABANK Corporation and its subsidiaries. IAM provides wealth management advisory services for commercial and private banking clients. CDE is engaged in the purchase of tax credits.

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The main offices of IBERIABANK Corporation and IBERIABANK are located at 200 West Congress Street, Lafayette, Louisiana 70501 (Telephone Number: (337) 521-4003).

Gibraltar

Gibraltar Private Bank & Trust Company is a federal savings bank headquartered in Coral Gables, Florida. Gibraltar has eight bank branch offices, with five in Southeast Florida, one in Key Largo, Florida, one in Naples, Florida, and one in New York, New York. As of September 30, 2017, Gibraltar had total unaudited assets of $1.6 billion, total unaudited deposits of $1.1 billion and total unaudited shareholders’ equity of $144.4 million.

The main office of Gibraltar is located at 55 Alhambra Plaza, Coral Gables, Florida 33134 (Telephone Number: (305) 476-1982).

Background of the Merger

As a part of the ongoing consideration and evaluation of Gibraltar’s long-term prospects and strategies, Gibraltar’s board of directors and senior management regularly reviewed and assessed the business strategies and objectives of Gibraltar. These evaluations and strategic discussions have focused on, among other things, the business environment facing financial institutions in general and smaller, Florida-based institutions such as Gibraltar in particular, as well as the then-current regulatory environment and the pace of consolidation in the financial services industry. With the goal of enhancing value for Gibraltar’s stockholders, the board of directors and senior management considered various strategic opportunities and challenges, and considered various strategic options potentially available to Gibraltar, such as organic growth, a business combination involving Gibraltar and one or more financial institutions, a capital raise, and a possible sale of Gibraltar to a larger financial institution.

To that end, on February 12, 2013, Gibraltar engaged Sandler O’Neill, an investment bank with significant expertise in financial institutions, as Gibraltar’s financial advisor to provide advice on such strategic options and directed Sandler O’Neill to contact various parties, selected by management and Sandler O’Neill after consultation with the board of directors and based on their assessed ability and level of interest in a potential transaction with Gibraltar, to discuss potential strategic options for Gibraltar. Following Sandler O’Neill’s engagement and as part of that process, various parties, including IBERIABANK Corporation, were contacted by Sandler O’Neill to consider all of the various strategic options.

On May 9, 2014, Sandler O’Neill, on behalf of Gibraltar, entered into a confidentiality and non-disclosure agreement with IBERIABANK Corporation regarding a potential combination with Gibraltar. IBERIABANK Corporation reviewed certain information about Gibraltar. IBERIABANK decided not to proceed with full due diligence at that time based on then strategic priorities and other considerations , but Adolfo Henriques, Gibraltar’s Chairman, remained in periodic dialogue with Daryl G. Byrd, IBERIABANK Corporation’s President and Chief Executive Officer, and John R. Davis, IBERIABANK Corporation’s then-Director of Financial Strategy, Mergers and Acquisitions and Investor Relations, over the course of the next three years. During this period, Gibraltar also executed confidentiality agreements with a number of other financial institutions and provided non-public information to those institutions. Several of those institutions made initial acquisition proposals but none led to final proposals or the signing of a definitive agreement.

On June 26, 2017, the OCC terminated its Consent Order with Gibraltar relating to certain compliance matters. Thereafter, Gibraltar and IBERIABANK Corporation engaged in further discussions regarding a potential business combination, and on August 17, 2017, IBERIABANK Corporation submitted a letter to Mr. Henriques containing proposed preliminary terms for a potential merger transaction, which terms contemplated the acquisition of Gibraltar for an equity value in the range of $230 million to $250 million with consideration to be paid in the form of IBERIABANK Corporation common stock and with a fixed exchange ratio (except to the extent IBERIABANK Corporation’s common stock price increases or decreases by 15% from the agreed-upon value, in which case the exchange ratio would fluctuate and the value to Gibraltar’s stockholders would become fixed). The letter additionally contemplated that the parties would enter into a 60-day exclusive negotiation period.

Following discussions among the parties, on August 21, 2017, Sandler O’Neill communicated telephonically to Mr. Henriques revised preliminary terms proposed by IBERIABANK Corporation for a potential merger transaction, which revisions contemplated a 40-day exclusivity period and the discussion of mutually agreeable arrangements for employee retention in light of a transaction. Mr. Henriques had extensive discussions with Sandler O’Neill regarding other possible

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opportunities, and agreed with Sandler that the terms outlined by IBERIABANK Corporation presented the best alternative for Gibraltar’s shareholders. Mr. Henriques convened a conference call with the board on the same day and, after a discussion regarding the revised preliminary proposed terms and the likelihood of other opportunities, the board unanimously approved exploring the transaction on the terms that had been outlined, and approved entering into an exclusivity agreement with IBERIABANK Corporation.

On August 22, 2017, IBERIABANK Corporation presented a written proposal in the form of a letter of intent to Gibraltar confirming the terms of a potential merger of Gibraltar into IBERIABANK that had been orally discussed. On August 25, 2017, Gibraltar and IBERIABANK Corporation entered into an exclusivity agreement whereby Gibraltar agreed to allow IBERIABANK Corporation to conduct due diligence for a period of 40 days (subject to possible extension), during which time Gibraltar would negotiate exclusively with IBERIABANK Corporation regarding a possible acquisition.

Gibraltar received a due diligence request list from IBERIABANK Corporation on August 22, 2017 and proceeded to provide substantially all the information that was requested. IBERIABANK Corporation commenced its due diligence review. The parties had frequent discussions, and requests for clarification and additional information were timely responded to or provided. These discussion and requests continued throughout the entire due diligence period.

On September 14, 2017, Gibraltar received a draft merger agreement from IBERIABANK Corporation. The terms of the merger agreement were within the parameters of the proposal. Mr. Henriques met with representatives of Broad and Cassel LLP, outside counsel to Gibraltar (which we refer to as “Broad and Cassel”), on September 26, 2017 to discuss the merger agreement. On September 28, 2017, representatives of Broad and Cassel provided comments to the merger agreement to representatives of Simpson Thacher & Bartlett LLP, outside counsel to IBERIABANK Corporation (which we refer to as “Simpson Thacher”). Later that day, representatives of Broad and Cassel and Simpson Thacher conferred by telephone regarding these comments. Issues under discussion included the representations and warranties to be given by Gibraltar in the merger agreement, certain covenants governing the conduct of Gibraltar’s business after signing the merger agreement and before closing, whether Gibraltar would have the right to terminate the merger agreement in the event of a substantial decline in the price of IBERIABANK Corporation common stock, and the circumstances under which a termination fee would be payable by Gibraltar.

On September 29, 2017, Sandler O’Neill provided to IBERIABANK Corporation a reverse due diligence request list.

On October 6, 2017, IBERIABANK Corporation requested and was granted an extension of the exclusivity period until October 22, 2017. Counsel to IBERIABANK Corporation also on October 6, 2017 provided Gibraltar’s counsel with a revised draft of the merger agreement and counsel to each party conferred by telephone to discuss the merger agreement.

On October 9, 2017, Gibraltar’s executive management again met with outside counsel to undertake an additional review of the merger agreement, including the representations, warranties and covenants. Gibraltar and Broad and Cassel also commenced preparation of the disclosure letter that Gibraltar was to deliver in conjunction with the execution of the merger agreement.

On October 11, 2017, Sandler O’Neill on behalf of Gibraltar, and IBERIABANK Corporation, entered into an amendment to their existing confidentiality and non-disclosure agreement to facilitate the sharing of non-public information regarding IBERIABANK Corporation requested by Gibraltar. Thereafter, on October 12, 2017, representatives of IBERIABANK Corporation, Gibraltar and its financial and legal advisors held a reverse due diligence conference call. Representatives of Broad and Cassel, Gibraltar management and Sandler O’Neill were also provided access to a data room containing the documents and information delivered by IBERIABANK Corporation in response to the reverse due diligence request list of September 29, 2017.

Also on October 12, 2017, representatives of Simpson Thacher provided a draft form of voting agreement for execution by the Gibraltar directors in connection with the merger agreement to representatives of Broad and Cassel. On that same day, representatives of Broad and Cassel sent to representatives of Simpson Thacher an initial draft of the disclosure letter to be delivered by Gibraltar in conjunction with the merger agreement. Additional drafts to Gibraltar’s disclosure letter were circulated to IBERIABANK Corporation during the next week. Representatives of Broad and Cassel provided initial comments on the form of voting agreement to representatives of Simpson Thacher on October 13, 2017.

Thereafter, the parties continued to have additional discussions and continued to negotiate and finalize the merger agreement and the other transaction documents.

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On October 14, 2017, representatives of Broad and Cassel received an updated draft merger agreement from representatives of Simpson Thacher, which Broad and Cassel then distributed to all the members of Gibraltar’s board of directors.

On October 16, 2017, the board of directors of Gibraltar held a meeting to consider the proposed transaction with IBERIABANK Corporation. At this meeting, the board received presentations from representatives of Broad and Cassel and Sandler O’Neill, and discussed the proposed transaction with senior management. Representatives of Broad and Cassel also reviewed with the directors their fiduciary duty to Gibraltar’s stockholders under applicable law and reviewed the terms and conditions of the merger agreement, the merger and the voting agreements to be signed in connection with the merger agreement. Representatives of Sandler O’Neill reviewed the financial aspects of the proposed merger and rendered to Gibraltar’s board an opinion, dated October 16, 2017, that, as of such date and subject to the procedures followed, assumptions made, matters considered, and qualifications and limitations on the review undertaken by Sandler O’Neill as set forth in such opinion, the exchange ratio in the proposed merger was fair, from a financial point of view, to the holders of Gibraltar’s common stock. Following a substantive discussion among members of Gibraltar’s board of directors, including consideration of the factors described under “—Gibraltar’s Reasons for the Merger; Recommendation of the Gibraltar Board of Directors” below in this proxy statement/prospectus, Gibraltar’s board of directors unanimously determined that the merger agreement and the merger were advisable and in the best interests of Gibraltar and its stockholders, approved and adopted the merger agreement and the merger, and recommended that the merger agreement and the merger be submitted to Gibraltar’s stockholders for approval, subject to finalization of all provisions of the merger agreement and completion of Gibraltar’s and IBERIABANK Corporation’s disclosure letters.

On October 17, 2017, the IBERIABANK Corporation board of directors met and approved the merger agreement and the transactions contemplated thereby, subject to finalization of all provisions of the merger agreement and completion of Gibraltar’s and IBERIABANK Corporation’s disclosure letters.

On October 17, 18, and 19, 2017, additional and final revisions to the merger agreement and form of voting agreement were circulated between Gibraltar and IBERIABANK Corporation and their respective counsel, and to Gibraltar’s directors, which drafts addressed, among other things, the treatment of Gibraltar’s restricted stock awards and the representations and warranties of Gibraltar. Representatives of Broad and Cassel communicated by email and telephone with the directors regarding these revisions. Further and final revisions to Gibraltar’s disclosure letter were also provided to IBERIABANK Corporation.

On October 19, 2017, Gibraltar, IBERIABANK Corporation and IBERIABANK signed the merger agreement and the Gibraltar directors, IBERIABANK Corporation and IBERIABANK signed the voting agreements. IBERIABANK Corporation issued a press release announcing the transaction that afternoon.

Gibraltar’s Reasons for the Merger; Recommendation of the Gibraltar Board of Directors

Gibraltar’s board of directors has determined that the merger is fair to, and in the best interests of, Gibraltar’s stockholders. In approving the merger agreement, Gibraltar’s board of directors consulted with Sandler O’Neill with respect to the financial aspects of the merger, and with its outside legal counsel as to its legal duties and the terms of the merger agreement. In arriving at its determination, Gibraltar’s board of directors also considered a number of factors, including the following:

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Gibraltar’s board of directors also considered potential risks relating to the merger, including the following:

The discussion of the information and factors considered by Gibraltar’s board of directors is not exhaustive, but does include the material factors considered by Gibraltar’s board of directors in approving the merger. The above factors were not presented in any order of priority. In reaching its determination, the Gibraltar board of directors did not assign any relative or specific weights to different factors, and individual directors may have weighed certain factors differently than other directors.

Gibraltar’s board of directors acknowledged there can be no assurance about future results, including results expected or considered in the factors listed above. However, Gibraltar’s board of directors concluded the potential positive factors outweighed the potential risks of completing the merger. Based on the reasons stated, Gibraltar’s board of directors determined that the merger is in the best interest of Gibraltar’s stockholders, and therefore the board of directors of Gibraltar unanimously approved the merger agreement and the merger.

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All members of Gibraltar’s board of directors have entered into voting agreements in which each has agreed to vote the shares of Gibraltar common stock over which they have voting authority in favor of the adoption and approval of the merger proposal.

Gibraltar’s board of directors unanimously recommends that Gibraltar’s stockholders vote “FOR” the adoption and approval of the merger proposal.

Opinion of Gibraltar’s Financial Advisor

Gibraltar retained Sandler O’Neill & Partners, L.P. (which we refer to as “Sandler O’Neill”) to act as an independent financial advisor to Gibraltar’s board of directors in connection with Gibraltar’s consideration of a possible business combination. Gibraltar selected Sandler O’Neill because Sandler O’Neill is a nationally recognized investment banking firm whose principal business specialty is financial institutions. In the ordinary course of its investment banking business, Sandler O’Neill is regularly engaged in the valuation of financial institutions and their securities in connection with mergers and acquisitions and other corporate transactions.

Sandler O’Neill acted as an independent financial advisor in connection with the proposed transaction and participated in certain of the negotiations leading to the execution of the merger agreement. At the October 16, 2017 meeting at which Gibraltar’s board of directors considered and discussed the terms of the merger agreement and the merger, Sandler O’Neill delivered to Gibraltar’s board of directors its oral opinion, which was subsequently confirmed in writing, to the effect that, as of October 16, 2017, the exchange ratio provided for in the merger agreement was fair to the holders of Gibraltar common stock from a financial point of view. The full text of Sandler O’Neill’s opinion is attached as Appendix C to this proxy statement/prospectus. The opinion outlines the procedures followed, assumptions made, matters considered and qualifications and limitations on the review undertaken by Sandler O’Neill in rendering its opinion. The description of the opinion set forth below is qualified in its entirety by reference to the full text of the opinion. Holders of Gibraltar common stock are urged to read the entire opinion carefully in connection with their consideration of the proposed merger.

Sandler O’Neill’s opinion speaks only as of the date of the opinion. The opinion was directed to Gibraltar’s board of directors in connection with its consideration of the merger agreement and the merger and does not constitute a recommendation to any stockholder of Gibraltar as to how any such stockholder should vote at any meeting of stockholders called to consider and vote upon the approval of the merger agreement and the merger. Sandler O’Neill’s opinion was directed only to the fairness, from a financial point of view, of the exchange ratio to the holders of Gibraltar common stock and does not address the underlying business decision of Gibraltar to engage in the merger, the form or structure of the merger or any other transactions contemplated in the merger agreement, the relative merits of the merger as compared to any other alternative transactions or business strategies that might exist for Gibraltar or the effect of any other transaction in which Gibraltar might engage. Sandler O’Neill did not express any opinion as to the fairness of the amount or nature of the compensation to be received in the merger by any officer, director or employee of Gibraltar or IBERIABANK Corporation, or any class of such persons, if any, relative to the compensation to be received in the merger by any other stockholder, including the merger consideration to be received by the holders of Gibraltar common stock. Sandler O’Neill’s opinion was approved by Sandler O’Neill’s fairness opinion committee.

In connection with its opinion, Sandler O’Neill reviewed and considered, among other things:

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Sandler O’Neill also discussed with certain members of the management of Gibraltar and its representatives the business, financial condition, results of operations and prospects of Gibraltar and held similar discussions with certain members of the management of IBERIABANK Corporation and its representatives regarding the business, financial condition, results of operations and prospects of IBERIABANK Corporation.

In performing its review, Sandler O’Neill relied upon the accuracy and completeness of all of the financial and other information that was available to and reviewed by Sandler O’Neill from public sources, that was provided to Sandler O’Neill by Gibraltar or IBERIABANK Corporation or their respective representatives, or that was otherwise reviewed by Sandler O’Neill, and Sandler O’Neill assumed such accuracy and completeness for purposes of rendering its opinion without any independent verification or investigation. Sandler O’Neill relied on the assurances of the respective managements of Gibraltar and IBERIABANK Corporation that they were not aware of any facts or circumstances that would make any of such information inaccurate or misleading. Sandler O’Neill was not asked to and did not undertake an independent verification of any of such information and Sandler O’Neill did not assume any responsibility or liability for the accuracy or completeness thereof. Sandler O’Neill did not make an independent evaluation or perform an appraisal of the specific assets, the collateral securing assets or the liabilities (contingent or otherwise) of Gibraltar or IBERIABANK Corporation or any of their respective subsidiaries, nor was Sandler O’Neill furnished with any such evaluations or appraisals. Sandler O’Neill rendered no opinion or evaluation on the collectability of any assets or the future performance of any loans of Gibraltar or IBERIABANK Corporation. Sandler O’Neill did not make an independent evaluation of the adequacy of the allowance for loan losses of Gibraltar or IBERIABANK Corporation, or of the combined entity after the merger, and Sandler O’Neill did not review any individual credit files relating to Gibraltar or IBERIABANK Corporation. Sandler O’Neill assumed, with Gibraltar’s consent, that the respective allowances for loan losses for both Gibraltar and IBERIABANK Corporation were adequate to cover such losses and would be adequate on a pro forma basis for the combined entity.

In preparing its analyses, Sandler O’Neill used certain internal financial projections for Gibraltar for the years ending December 31, 2017 through December 31, 2021, as provided by the senior management of Gibraltar. In addition, Sandler O’Neill used publicly available consensus mean analyst net income estimates for IBERIABANK Corporation for the year ending December 31, 2017 and mean analyst consensus earnings per share and balance sheet estimates for IBERIABANK Corporation for the years ending December 31, 2018 and December 31, 2019, as confirmed by the senior management of IBERIABANK Corporation, as well as estimated long-term earnings per share and balance sheet growth rates for the years ending December 31, 2020 and December 31, 2021 and estimated dividends per share for the years ending December 31, 2017 through December 31, 2021, as provided by the senior management of IBERIABANK Corporation. Sandler O’Neill also received and used in its pro forma analyses certain assumptions relating to purchase accounting adjustments, cost savings and transaction expenses as well as net income estimates for Gibraltar for the three quarters ending December 31, 2018 and the years ending December 31, 2019 and December 31, 2020 with a long term estimated earnings growth rate for the years thereafter, as provided by the senior management of IBERIABANK Corporation. With respect to the foregoing information, the respective managements of Gibraltar and IBERIABANK Corporation confirmed to Sandler O’Neill that such information reflected (or, in the case of the publicly available consensus mean analyst net income, earnings per share

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and balance sheet estimates referred to above, were consistent with) the best currently available projections, estimates and judgments of those respective managements as to the future financial performance of Gibraltar and IBERIABANK Corporation, respectively, and the other matters covered thereby, and Sandler O’Neill assumed that the future financial performance reflected in such information would be achieved. Sandler O’Neill expressed no opinion as to such information, or the assumptions on which such information was based. Sandler O’Neill also assumed that there had been no material change in the respective assets, financial condition, results of operations, business or prospects of Gibraltar or IBERIABANK Corporation since the date of the most recent financial statements made available to Sandler O’Neill. Sandler O’Neill assumed in all respects material to its analysis that Gibraltar and IBERIABANK Corporation would remain as going concerns for all periods relevant to Sandler O’Neill’s analysis.

Sandler O’Neill also assumed, with Gibraltar’s consent, that (i) each of the parties to the merger agreement would comply in all material respects with all material terms and conditions of the merger agreement and all related agreements, that all of the representations and warranties contained in such agreements were true and correct in all material respects, that each of the parties to such agreements would perform in all material respects all of the covenants and other obligations required to be performed by such party under such agreements and that the conditions precedent in such agreements were not and would not be waived, (ii) in the course of obtaining the necessary regulatory or third party approvals, consents and releases with respect to the merger, no delay, limitation, restriction or condition would be imposed that would have an adverse effect on Gibraltar, IBERIABANK Corporation or the merger or any related transaction, (iii) the merger and any related transactions would be consummated in accordance with the terms of the merger agreement without any waiver, modification or amendment of any material term, condition or agreement thereof and in compliance with all applicable laws and other requirements, and (iv) the merger would qualify as a tax-free reorganization for federal income tax purposes. Finally, with Gibraltar’s consent, Sandler O’Neill relied upon the advice that Gibraltar had received from its legal, accounting and tax advisors as to all legal, accounting and tax matters relating to the merger and the other transactions contemplated by the merger agreement. Sandler O’Neill expressed no opinion as to any such matters.

Sandler O’Neill’s opinion was necessarily based on financial, economic, market and other conditions as in effect on, and the information made available to Sandler O’Neill as of, the date thereof. Events occurring after the date thereof could materially affect Sandler O’Neill’s opinion. Sandler O’Neill has not undertaken to update, revise, reaffirm or withdraw its opinion or otherwise comment upon events occurring after the date thereof. Sandler O’Neill expressed no opinion as to the trading value of IBERIABANK Corporation common stock at any time or what the value of IBERIABANK Corporation common stock would be once it is actually received by the holders of Gibraltar common stock.

In rendering its opinion, Sandler O’Neill performed a variety of financial analyses. The summary below is not a complete description of the analyses underlying Sandler O’Neill’s opinion or the presentation made by Sandler O’Neill to Gibraltar’s board of directors, but is a summary of all material analyses performed and presented by Sandler O’Neill. The summary includes information presented in tabular format. In order to fully understand the financial analyses, these tables must be read together with the accompanying text. The tables alone do not constitute a complete description of the financial analyses. The preparation of a fairness opinion is a complex process involving subjective judgments as to the most appropriate and relevant methods of financial analysis and the application of those methods to the particular circumstances. The process, therefore, is not necessarily susceptible to a partial analysis or summary description. Sandler O’Neill believes that its analyses must be considered as a whole and that selecting portions of the factors and analyses to be considered without considering all factors and analyses, or attempting to ascribe relative weights to some or all such factors and analyses, could create an incomplete view of the evaluation process underlying its opinion. Also, no company included in Sandler O’Neill’s comparative analyses described below is identical to Gibraltar or IBERIABANK Corporation and no transaction is identical to the merger. Accordingly, an analysis of comparable companies or transactions involves complex considerations and judgments concerning differences in financial and operating characteristics of the companies and other factors that could affect the public trading values or merger transaction values, as the case may be, of Gibraltar and IBERIABANK Corporation and the companies to which they are being compared. In arriving at its opinion, Sandler O’Neill did not attribute any particular weight to any analysis or factor that it considered. Rather, Sandler O’Neill made qualitative judgments as to the significance and relevance of each analysis and factor. Sandler O’Neill did not form an opinion as to whether any individual analysis or factor (positive or negative) considered in isolation supported or failed to support its opinion, rather, Sandler O’Neill made its determination as to the fairness of the exchange ratio on the basis of its experience and professional judgment after considering the results of all its analyses taken as a whole.

In performing its analyses, Sandler O’Neill also made numerous assumptions with respect to industry performance, business and economic conditions and various other matters, many of which are beyond the control of Gibraltar, IBERIABANK Corporation and Sandler O’Neill. The analyses performed by Sandler O’Neill were not necessarily indicative

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of actual values or future results, both of which could be significantly more or less favorable than suggested by such analyses. Sandler O’Neill prepared its analyses solely for purposes of rendering its opinion and provided such analyses to Gibraltar’s board of directors at its October 16, 2017 meeting. Estimates on the values of companies do not purport to be appraisals or necessarily reflect the prices at which companies or their securities may actually be sold. Such estimates are inherently subject to uncertainty and actual values may be materially different. Accordingly, Sandler O’Neill’s analyses do not necessarily reflect the value of Gibraltar common stock or the prices at which IBERIABANK Corporation common stock may be sold at any time. The analyses of Sandler O’Neill and its opinion were among a number of factors taken into consideration by Gibraltar’s board of directors in making its determination to approve the merger agreement and should not be viewed as determinative of the exchange ratio or the decision of Gibraltar’s board of directors or management with respect to the fairness of the merger. The type and amount of consideration payable in the merger were determined through negotiation between Gibraltar and IBERIABANK Corporation.

Summary of Exchange Ratio and Implied Transaction Metrics. Sandler O’Neill reviewed the financial terms of the proposed merger. Subject to certain adjustments, as more fully described in the merger agreement, at closing, each share of Gibraltar common stock and common stock equivalents issued and outstanding prior to the effective time, except for certain shares of Gibraltar common stock as specified in the merger agreement, will receive 1.9749 shares of the common stock of IBERIABANK Corporation. Based on 1,411,645 shares of Gibraltar common stock and common stock equivalents issued and outstanding, as of June 30, 2017, the 10-day volume weighted average closing price of IBERIABANK Corporation common stock ended October 13, 2017 of $82.50 and a per share exchange ratio of 1.9749, Sandler O’Neill calculated an implied transaction price per share for Gibraltar common stock of $162.93 and an aggregate implied transaction value of approximately $234.9 million. Based upon historical financial information for Gibraltar as of or for the last twelve months (“LTM”) ended June 30, 2017 and estimated net income for the years ending December 31, 2017 and December 31, 2018, as provided by Gibraltar senior management, Sandler O’Neill calculated the following implied transaction metrics.

Gibraltar Comparable Company Analyses. Sandler O’Neill used publicly available information to compare selected financial information for Gibraltar with a group of financial institutions selected by Sandler O’Neill (the “Gibraltar Peer Group”). The Gibraltar Peer Group consisted of banks and thrifts with publicly traded securities listed on the NASDAQ, NYSE or NYSE Market headquartered in the Southeast Region with assets between $1.0 billion and $2.5 billion, excluding announced merger targets. The Gibraltar Peer Group consisted of the following companies:

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The analysis compared publicly available financial information for Gibraltar as of or for the last twelve months ended June 30, 2017 with the corresponding publicly available data for the Gibraltar Peer Group as of or for the last twelve months ended June 30, 2017, with pricing data as of October 13, 2017. The table below sets forth the data for Gibraltar and the high, low, median and mean data for the Gibraltar Peer Group.

Gibraltar Net Present Value Analyses. Sandler O’Neill performed an analysis that estimated the net present value per share of Gibraltar common stock assuming Gibraltar performed in accordance with internal financial projections for the years ending December 31, 2017 through December 31, 2021, as provided by the senior management of Gibraltar. To approximate the terminal value of a share of Gibraltar common stock at December 31, 2021, Sandler O’Neill applied price to 2021 earnings per share multiples ranging from 15.0x to 25.0x and price to December 31, 2021 tangible book value per share multiples ranging from 135% to 235%. The terminal values were then discounted to present values using different discount rates ranging from 9.0% to 15.0% which were chosen to reflect different assumptions regarding required rates of return of holders or prospective buyers of Gibraltar common stock. As illustrated in the following tables, the analysis indicated an imputed range of values per share of Gibraltar common stock of $64.27 to $136.33 when applying multiples of earnings per share, and $93.27 to $206.63 when applying multiples of tangible book value per share.

Earnings Per Share Multiples

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Tangible Book Value Per Share Multiples

Sandler O’Neill also considered and discussed with the Gibraltar board of directors how this analysis would be affected by changes in the underlying assumptions, including variations with respect to net income. To illustrate this impact, Sandler O’Neill performed a similar analysis assuming Gibraltar’s net income varied from 15% above projections to 15% below projections. This analysis resulted in the following range of per share values for Gibraltar common stock, applying the price to 2021 earnings per share multiples range of 15.0x to 25.0x referred to above and a discount rate of 12.90%.

Earnings Per Share Multiples

Sandler O’Neill noted that the net present value analysis is a widely used valuation methodology, but the results of such methodology are highly dependent upon the numerous assumptions that must be made, and the results thereof are not necessarily indicative of actual values or future results.

Analysis of Selected Merger Transactions. Sandler O’Neill reviewed two groups of selected merger and acquisition transactions involving U.S. banks and thrifts (the “Nationwide Precedent Transactions” and the “Florida Precedent Transactions”). The Nationwide Precedent Transactions group consisted of bank and thrift transactions announced between January 1, 2016 and October 13, 2017 with disclosed deal values involving targets with assets between $500 million and $3.0 billion, and last twelve months return on average assets ratios equal to or less than 0.50%. The Florida Precedent Transactions group consisted of bank and thrifts transactions announced between January 1, 2014 and October 13, 2017 with disclosed deal values involving targets headquartered in Florida with total assets between $500 million and $5.0 billion, and last twelve months return on average assets ratios equal to or less than 0.50%.

The Nationwide Precedent Transactions group was composed of the following transactions:

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The Florida Precedent Transactions group was composed of the following transactions:

Using the latest publicly available information prior to the announcement of the relevant transaction, Sandler O’Neill reviewed the following transaction metrics: transaction price to LTM earnings per share, transaction price to tangible book value per share and tangible book value premium to core deposits. Sandler O’Neill compared the indicated transaction multiples for the merger to the high, low, mean and median multiples of the Nationwide Precedent Transactions group as well the Florida Precedent Transactions group, but excluding multiples over 50.0x.

IBERIABANK Corporation Comparable Company Analyses. Sandler O’Neill used publicly available information to compare selected financial information for IBERIABANK Corporation with a group of financial institutions selected by Sandler O’Neill (the “IBERIABANK Corporation Peer Group”). The IBERIABANK Corporation Peer Group consisted of banks and thrifts with publicly traded securities listed on the NASDAQ, NYSE or NYSE Market, headquartered in the Southeast and Southwest Regions with assets between $10.0 billion and $30.0 billion, excluding announced merger targets. The IBERIABANK Corporation Peer Group consisted of the following companies:

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The analysis compared publicly available financial information for IBERIABANK Corporation as of or for the last twelve months ended June 30, 2017 with the corresponding publicly available data for the IBERIABANK Corporation Peer Group as of or for the last twelve months ended June 30, 2017 (unless otherwise noted), with pricing data as of October 13, 2017. The table below sets forth the data for IBERIABANK Corporation and the high, low, median and mean data for the IBERIABANK Corporation Peer Group.