SUMMARY

This summary provides a brief overviewhighlights selected information from this joint proxy statement/prospectus and may not contain all of the key aspects of the reorganization agreement,information that is important to you regarding the merger the Tradition special shareholder meeting and the offering of shares of Prosperity common stock to Tradition shareholders in connection with the merger. This summary identifies those aspects thatrelated matters. Prosperity and Tradition believe may be most significant to the Tradition shareholders. WeLegacy urge you to carefully read this entire document and the other documents we referinformation that is referred to in this document.joint proxy statement/prospectus or contained in the reports and documents incorporated by reference in this joint proxy statement/prospectus. These documents will give you a more complete description of the transaction we are proposing.items for consideration at the special meeting. For more information about Prosperity and Legacy, see “Where You Can Find More Information” on page 90. We152. Prosperity and Legacy have included page references in this summary to direct you to other places in this joint proxy statement/prospectus where you can find a more complete description of the topics wethat Prosperity and Legacy have summarized.

The Companies (page 131)

Prosperity Bancshares, Inc.

Prosperity Bank Plaza

4295 San Felipe

Houston, Texas 77027

(713) 693-9300(281)269-7199

www.prosperitybankusa.com

Prosperity Bancshares, Inc.^® (“Prosperity”) was formed in 1983 as a vehicle to acquire the former Allied Bank in Edna, Texas, which was chartered in 1949 as The First National Bank of Edna and is now known as Prosperity Bank. Prosperity is a Texas corporation is aand registered financial holding company pursuant tothat derives substantially all of its revenues and income from the Gramm-Leach-Bliley Act andoperation of its bank holding company registered under thesubsidiary, Prosperity Bank Holding Company Act of 1956, as amended (the “BHC Act”^® (“Prosperity Bank”). Through Prosperity Bank its wholly owned subsidiary bank,provides a wide array of financial products and services to small andmedium-sized businesses and consumers. As of June 30, 2019, Prosperity conducts a complete range of commercial and personalBank operated 243 full service banking activities. Prosperity currently operates a total of two hundred forty-four (244) full-service banking centers, with sixty-one (61)locations: 65 in the Houston area, including The Woodlands and Huntsville; thirty (30)Woodlands; 30 in the South Texas area, including Corpus Christi and Victoria; thirty-seven (37)33 in the Dallas/Fort Worth area; twenty-two (22)22 in the East Texas area; thirty (30)29 in the Central Texas area, including Austin and San Antonio; thirty-four (34)34 in the West Texas area, including Lubbock, Midland/OdessaMidland-Odessa and Abilene; sixteen (16)16 in the Bryan/College Station area; six (6)6 in the Central Oklahoma areaarea; and eight (8)8 in the Tulsa, Oklahoma area. As of September 30, 2015,Prosperity’s common stock is traded on a consolidated basis, Prosperity had total assets of $21.57 billion, total loans of $9.20 billion, total deposits of $16.94 billion and shareholders’ equity of $3.41 billion.the NYSE under the symbol “PB.”

Tradition Bancshares,LegacyTexas Financial Group, Inc.

5501 Bissonnet5851 Legacy Circle

Houston,Plano, Texas 7708175024

(713) 666-2511(972)578-5000

Tradition Bancshares,www.legacytexas.com

LegacyTexas Financial Group, Inc. (“Legacy”) is a Maryland corporation and registered bank holding company. LegacyTexas Bank (“Legacy Bank”), a Texas corporation,banking association, is Legacy’s wholly owned principal operating subsidiary. The principal business of Legacy consists of attracting retail deposits from the general public and the business community and investing those funds, along with borrowed funds, in commercial real estate loans, secured and unsecured commercial and industrial loans, as well as permanent loans secured by first and second mortgages onone- to four-family residences and consumer loans. Additionally, Legacy Bank’s Warehouse Purchase Program allows mortgage banking company customers to closeone- to four-family real estate loans in their own name and manage their cash flow needs until the loans are sold to investors. Legacy’s operating revenues are derived principally from interest earned on interest-earning assets, including loans and investment securities, and service charges and fees on deposits and other account services. Legacy’s primary sources of funds are deposits, FHLB advances and other borrowings, and payments received on loans and securities. Legacy offers a bank holding company registeredvariety of deposit accounts that provide a wide range of interest rates and terms,

generally including savings, money market, certificate of deposit and demand accounts. At December 31, 2018, in addition to its executive offices, Legacy had three administrative offices, 42 full-service branches, one commercial loan production office located in Houston, Texas and a Warehouse Purchase Program office located in Littleton, Colorado. Legacy’s common stock is traded on the NASDAQ under the BHC Act and the holding company for Tradition Bank. Tradition Bank operates seven (7) banking offices in the Houston, Texas area, including its main office in Bellaire, three (3) banking centers in Katy and one (1) banking center in The Woodlands. As of September 30, 2015, Tradition had, on a consolidated basis, total assets of $540.6 million, total loans of $239.2 million, total deposits of $483.8 million and shareholders’ equity of $46.3 million.symbol “LTXB.”

Proposed Merger of Tradition into Prosperity(page 101)

We have attached theThe reorganization agreement is attached to this documentjoint proxy statement/prospectus asAppendix A. Please read the entire reorganization agreement. It is the legal document that governs the merger.

We proposeTerms of the Merger (page 61)

The reorganization agreement provides for the merger of Legacy with and into Prosperity, with Prosperity being the surviving corporation following the merger. Prosperity is the sole shareholder of Prosperity Bank, a Texas banking association, and Legacy is the sole shareholder of Legacy Bank, a Texas banking association. Pursuant to the reorganization agreement, immediately following the effectiveness of the merger, whereby TraditionLegacy Bank will merge with and into Prosperity. Prosperity will beBank, with Prosperity Bank being the surviving entitybank following the bank merger.

Merger Consideration (page 102)

At the effective time, each share of Legacy common stock (except for certain specified shares of Legacy common stock owned directly by Prosperity or Legacy, including shares of Legacy common stock held in the merger. Immediately following completiontreasury of the merger, the existing banking centers of Tradition Bank will become full-service banking centers of Prosperity Bank. We expect the merger to be completed during the fourth quarter of 2015 and effective on January 1, 2016, although delays could occur.

Set forth below is subject to decrease ina table showing the manner and underhypothetical implied value of the circumstancesmerger consideration based on a range of market prices for Prosperity common stock. The hypothetical implied value of the merger consideration set forth in the reorganization agreement if Tradition’s equity capital ontable below includes both the closing dateper share stock consideration and the per share cash consideration. Unlike the value of the merger is less than $42,700,000.

In addition, ifper share stock consideration, the average closing pricevalue of the Prosperity common stock for the five consecutive trading days ending on and including the fifth trading day prior to the closing date of the merger, which we refer to herein as the average closing price, exceeds $65.98, the exchange ratio or the per share cash consideration or a combinationis fixed (at $6.28 per share of the twoLegacy common stock) and will be decreased such that the aggregate value of the Prosperity common stock and cash equal no more than $83,845,220, as further described in this proxy statement/prospectus and the reorganization agreement.

The value of the total merger consideration you will receive therefore willnot fluctuate based on the market price of the Prosperity common stock. Further,The table does not reflect the fact that cash portionwill be paid instead of fractional shares.

The examples above are illustrative only. The value of the merger consideration is subject to adjustment as described above. Accordingly, youthat a Legacy stockholder actually receives will not knowbe based on the exact amountactual closing price on NYSE of cash or the valueProsperity common stock upon completion of the stock portionmerger, which may be outside the range of the amounts set forth above, and as a result, the actual value of the merger consideration youper share of Legacy common stock at closing may not be shown in the above table.

Treatment of Legacy Options (page 102)

At the effective time, subject to the terms and conditions of the reorganization agreement, each option granted by Legacy to purchase shares of Legacy common stock under the Legacy equity compensation plans will fully vest and be cancelled and converted into the right to receive the merger consideration with respect to a number of shares of Legacy common stock (rounded down to the nearest whole share) equal to the quotient of (x) the product of (A) the number of shares of Legacy common stock subject to such option multiplied by (B) the excess, if any, of (i) the sum of the per share stock consideration and the per share cash consideration over (ii) the exercise price per share of Legacy common stock under the option, divided by (y) the sum of the per share stock consideration and the per share cash consideration.

Treatment of Legacy Restricted Stock Awards and Performance Share Awards (page 102)

At the effective time, subject to the terms and conditions of the reorganization agreement, each unvested Legacy restricted stock award and performance share award will vest and be converted into the right to receive the merger consideration (with any performance-based vesting conditions applicable to such awards immediately prior to the effective time deemed satisfied at target performance levels) with respect to the number of shares of Legacy common stock subject to such restricted stock award or performance share award.

Recommendation of the Legacy Board and Its Reasons for the Merger (page 67)

Based on the reasons discussed elsewhere in this joint proxy statement/prospectus, the board of directors of Legacy believes that the merger is in the best interests of Legacy and the stockholders of Legacy and recommends that Legacy stockholders vote FOR the Legacy merger proposal, FOR the Legacy compensation proposal and FOR the Legacy adjournment proposal. For a discussion of the circumstances surrounding the merger and the factors considered by Legacy’s board of directors in approving the reorganization agreement, see the discussion beginning on page 61.

Recommendation of the Prosperity Board and Its Reasons for the Merger (page 69)

Based on the reasons discussed elsewhere in this joint proxy statement/prospectus, the board of directors of Prosperity believes that the merger is in the best interests of Prosperity and the shareholders of Prosperity and recommends that Prosperity shareholders vote FOR the Prosperity merger proposal and FOR the Prosperity adjournment proposal. For a discussion of the circumstances surrounding the merger and the factors considered by Prosperity’s board of directors in approving the reorganization agreement, see the discussion beginning on page 61.

Opinion of Legacy’s Financial Advisor (page 71;Appendix B)

At the meeting of the Legacy board of directors on June 14, 2019, Legacy’s financial advisor, J.P. Morgan Securities LLC (“J.P. Morgan”), rendered its oral opinion to the Legacy board of directors, subsequently confirmed in writing, that, as of such date and based upon and subject to the factors and assumptions set forth in its opinion, the merger consideration to be paid to the holders of Legacy common stock in the merger was fair, from a financial point of view, to such holders.

The full text of the J.P. Morgan opinion, which sets forth the assumptions made, matters considered and limits on the review undertaken, is attached asAppendix B to this joint proxy statement/prospectus and is incorporated herein by reference.The summary of the J.P. Morgan opinion set forth in this joint proxy statement/prospectus is qualified in its entirety by reference to the full text of such opinion.Legacy’s stockholders are urged to read the opinion in its entirety. J.P. Morgan’s written opinion was addressed to the Legacy board of directors (in its capacity as such) in connection with and for the purposes of its evaluation of the merger, was directed only to the merger consideration to be paid to the holders of Legacy common stock in the merger and did not address any other aspect of the merger. J.P. Morgan expressed no opinion as to the fairness of any consideration to be paid in connection with the merger when youto the holders of any other class of securities, creditors or other constituencies of Legacy or as to the underlying decision by Legacy to engage in the merger. The issuance of J.P. Morgan’s opinion was approved by a fairness committee of J.P. Morgan. The opinion does not constitute a recommendation to any stockholder of Legacy as to how such stockholder should vote with respect to the merger or any other matter.

For more information, see the section entitled “The Merger—Opinion of Legacy’s Financial Advisor” beginning on page 71 of this joint proxy statement/prospectus and the copy of the J.P. Morgan opinion included in this joint proxy statement/prospectus asAppendix B.

Opinion of Prosperity’s Financial Advisor (page 78;Appendix C)

In connection with the merger, Prosperity’s financial advisor, Keefe, Bruyette & Woods, Inc. (“KBW”), delivered a written opinion, dated June 14, 2019, to the Prosperity board of directors as to the fairness, from a financial point of view and as of the date of the opinion, to Prosperity of the aggregate merger consideration in the proposed merger. The full text of KBW’s opinion, which describes the procedures followed, assumptions

made, matters considered, and qualifications and limitations on the proposalreview undertaken by KBW in preparing the opinion, is attached asAppendix C to adoptthis joint proxy statement/prospectus.The opinion was for the information of, and was directed to, the Prosperity board of directors (in its capacity as such) in connection with its consideration of the financial terms of the merger. The opinion did not address the underlying business decision of Prosperity to engage in the merger or enter into the reorganization agreement or constitute a recommendation to the Prosperity board of directors in connection with the merger, and it does not constitute a recommendation to any holder of Prosperity common stock or any shareholder of any other entity as to how to vote in connection with the merger or any other matter.

For more information, see the section entitled “The Merger—Opinion of Prosperity’s Financial Advisor” beginning on page 78 of this joint proxy statement/prospectus and the copy of the KBW opinion included in this joint proxy statement/prospectus asAppendix C.

Financial Interests of Directors and Officers of Legacy in the Merger (page 93)

Legacy’s executive officers and directors may have interests in the merger that are different from, or in addition to, the interests of Legacy’s stockholders generally. Such interests include payments in connection with existing employment agreements and change in control severance plans with certain executive officers, Prosperity Bank and Legacy Bank entering into new employment agreements with Legacy Bank’s executive officers, and the right to indemnification and insurance coverage following the consummation of the merger. The members of the Legacy board of directors were aware of and considered these interests, among other matters, when they approved the reorganization agreement and recommended that Legacy stockholders approve the Legacy merger proposal. These interests are described in more detail under the section entitled “The Merger—Financial Interests of Directors and Officers of Legacy in the Merger” beginning on page 93.

The Prosperity Board of Directors After the Merger (page 98)

Effective immediately after the effective time, Prosperity will appoint Kevin Hanigan, Legacy’s current President and Chief Executive Officer, George Fisk, Legacy’s current vice chairman and Bruce Hunt, a current Legacy board member, to the Prosperity board of directors, each for a term expiring at the next annual meeting of the shareholders of Prosperity following the effective time and, in the case of each Mr. Fisk and Mr. Hunt, subject to his qualifying as an independent director. Prosperity will also nominate, and recommend that the Prosperity shareholders elect Messrs. Hanigan, Fisk and Hunt to the Prosperity board of directors at the first annual meeting of the shareholders of Prosperity following the effective time. Also effective immediately after the effective time, Prosperity Bank will appoint J. Mays Davenport, Legacy’s current Executive Vice President and Chief Financial Officer, to the board of directors of Prosperity Bank.

Prosperity Plans to Continue Payment of Quarterly Dividends (page 98)

As approved by Prosperity’s board of directors, Prosperity declared and paid a $0.34 per share dividend to holders of Prosperity common stock for the first three fiscal quarters of 2017 and a $0.36 per share dividend for the fourth fiscal quarter of 2017 and the first three fiscal quarters of 2018. Prosperity declared and paid a $0.41 per share dividend for the last fiscal quarter of 2018 and the first two fiscal quarters of 2019. On July 16, 2019, Prosperity declared a $0.41 per share dividend for the third fiscal quarter of 2019 with a record date of September 16, 2019.

Prosperity intends to continue to pay regular quarterly cash dividends on its common stock in the fourth fiscal quarter of 2019 and following the merger, when, as and if declared by Prosperity’s board of directors out of funds legally available for that purpose and subject to regulatory restrictions.

Issued Prosperity Shares Will Be Eligible for Trading (page 99)

Prosperity shares are listed for trading on the NYSE under the symbol “PB” and Legacy common stock is listed for trading on the NASDAQ under the symbol “LTXB.” Upon completion of the merger, Legacy common stock will no longer be listed for trading.

Under the reorganization agreement, Prosperity has agreed to file all documents required to be filed to have the shares of Prosperity common stock to be issued approved for listing on the NYSE prior to closing and to use its commercially reasonable efforts to effect such listing. The obligations of the parties to complete the merger are subject to such shares having been approved for listing on the NYSE and such approval having not been withdrawn or revoked.

Market Prices of Prosperity and Legacy Common Stock (page 134)

On June 14, 2019, the last trading day before the reorganization agreement was announced, Prosperity common stock closed at $67.24 per share. On September 13, 2019, the last practicable date before the date of this joint proxy statement/prospectus, Prosperity common stock closed at $71.04 per share.

On June 14, 2019, the last trading day before the merger was announced, Legacy common stock closed at $38.22 per share. On September 13, 2019, the last practicable date before the date of this joint proxy statement/prospectus, Legacy common stock closed at $43.61 per share.

The market price of Prosperity common stock and Legacy common stock will fluctuate prior to the merger. You should obtain the most recent closing price for Prosperity common stock and Legacy common stock on the NYSE and the NASDAQ, respectively, prior to deciding how to vote.

Dissenters’ Rights (page 99)

Under the MGCL, holders of Legacy common stock are not entitled to dissenters’ or appraisal rights in connection with the merger. Under the TBOC, holders of shares of Prosperity common stock are not entitled to dissenters’ or appraisal rights in connection with the merger or the share issuance.

Regulatory Approvals Required for the Merger (page 99)

The acquisition of Legacy and Legacy Bank by Prosperity requires the approval of the Board of Governors of the Federal Reserve System (which we refer to as the “Federal Reserve”), unless the requirement for such approval is waived by the Federal Reserve. On July 26, 2019, Prosperity filed the required documentation with the Federal Reserve Bank of Dallas to request a waiver of its approval, which was granted on August 13, 2019.

The merger of Legacy Bank with and into Prosperity Bank requires the approval of the Federal Deposit Insurance Corporation (which we refer to as the “FDIC”) and the Texas Department of Banking (which we refer to as the “TDB”). On July 15, 2019, Prosperity Bank and Legacy Bank filed the required applications with the FDIC and TDB.

Exchange Procedures (page 103)

After the effective time of the merger, the Legacy stockholders will receive a letter of transmittal and instructions from Computershare Investor Services, Inc., acting as Prosperity’s exchange and transfer agent, or the “exchange agent,” describing the procedures for surrendering their certificate or certificates representing shares of Legacy common stock (which we refer to as a “Legacy certificate,” which is deemed to include reference to book-entry accounts relating to the ownership of shares of Legacy common stock).

When you properly surrender your Legacy certificates or provide other satisfactory evidence of ownership, and return the letter of transmittal duly executed and completed in accordance with its instructions, the exchange agent will promptly cancel the surrendered stock certificates and deliver to you a notice specifying, among other things, the number of shares of Prosperity common stock, which will be solely in uncertificated book-entry form credited to the account of the holder of record as established in the Direct Registration System, and cash for fractional shares, if any, to which you are entitled under the reorganization agreement. No Prosperity stock certificates will be issued with respect to the Prosperity common stock to be issued under the reorganization agreement.

Please do not send Legacy or Prosperity any of your Legacy stock certificates until you receive these instructions, which will be as soon as practicable after the effective time.

Effective Time of the Merger (page 104)

The merger will become effective at the date and time specified in the certificate of merger to be filed with the Secretary of State of Texas and the certificate of merger to be filed with the Secretary of State of Maryland, which, unless otherwise agreed by Prosperity and Legacy, is expected to be 12:01 a.m. on the first day of the calendar month immediately following the calendar month in which all conditions are satisfied or (subject to applicable law) waived (other than conditions that by their nature can only be satisfied at the closing, but subject to the satisfaction or waiver thereof) or, if the foregoing occurs during the month of December 2019, 11:59 p.m. on December 31, 2019. It is anticipated that the bank merger will be effective immediately thereafter. If the stockholders of Legacy and shareholders of Prosperity approve the reorganization agreement at their respective special meetings, it is currently anticipated that the completion of the merger will occur in the fourth quarter of 2019, but completion of the merger could be delayed if there is a delay in obtaining the required regulatory approvals or in satisfying any other conditions to the merger.

Prosperity and Legacy cannot assure you that the necessary stockholder and shareholder and regulatory approvals will be obtained or that the other conditions to completion of the merger can or will be satisfied. See “Risk Factors—Risks Related to the Merger—The merger of Prosperity and Legacy may not be completed, may take longer than expected or may be subject to conditions imposed by government entities that are not presently anticipated or cannot be met.”

Conditions to Completion of the Merger (page 104)

The reorganization agreement contains a number of customary conditions to the obligations of Prosperity and Legacy to complete the merger that must be satisfied as of the closing date, including the approval of the reorganization agreement by the requisite Prosperity shareholder vote and the requisite Legacy stockholder vote, as well as the receipt of all required regulatory approvals.

Any condition to the completion of the merger may, to the extent permitted by law, be waived in writing by the party or parties to the reorganization agreement entitled to the benefit of such condition.

No Negotiation with Others (page 111)

Legacy agreed that it will not, and that it will cause each Legacy subsidiary and the respective employees, directors, officers, financial advisors, agents and other representatives of Legacy and each Legacy subsidiary (which we collectively refer to as the “Legacy representatives”) not to: (i) solicit, knowingly encourage or facilitate, initiate or participate in any negotiations or discussions with any third party (except for the limited purpose of notifying such person of the existence of thenon-solicitation provisions of the reorganization agreement) regarding an acquisition proposal, whether by acquisition, business combination, purchase of

securities or assets or otherwise; (ii) disclose to any third party any information concerning the business, properties, books or records of Legacy or any Legacy subsidiary in connection with any acquisition proposal; or (iii) cooperate with any third party to make any acquisition proposal. Promptly upon receipt of any unsolicited offer, Legacy will communicate to Prosperity the terms of any proposal or request for information and the identity of the parties involved.

Provided that it has complied with the foregoing provisions, if at any time after the date of the reorganization agreement and before the receipt of the requisite Legacy stockholder approval, Legacy and the Legacy representatives receive a bona fide, unsolicited written acquisition proposal, Legacy and the Legacy representatives may engage in negotiations and discussions with, and furnish any information and other access (so long as all such information and access has previously been made available to Prosperity or is made available to Prosperity before or concurrently with the time such information or access is made available to such person) to, any person making such acquisition proposal if, and only if, the Legacy board of directors determines in good faith, after consultation with outside legal and financial advisors, that (i) such acquisition proposal constitutes or is reasonably likely to become a superior proposal and (ii) the failure of the Legacy board of directors to furnish such information or access or enter into such discussions or negotiations would be inconsistent with its fiduciary duties under applicable law; but before furnishing any such information, Legacy has received from the person making such acquisition proposal an executed confidentiality agreement with terms at least as restrictive in all material respects on such person as the confidentiality agreement entered into with Prosperity, which confidentiality agreement may not prohibit Legacy from complying with the terms of the reorganization agreement.

Termination of the Reorganization Agreement (page 121)

Prosperity and Legacy can mutually agree at any time to terminate the reorganization agreement without completing the merger. In addition, either Prosperity or Legacy may terminate the reorganization agreement as follows:

In addition, Legacy may terminate the reorganization agreement if Prosperity or the Prosperity board of directors has failed to comply in any material respect with its obligations described under “—Prosperity Shareholder Meeting and Recommendation of the Prosperity Board of Directors.”

In addition, Prosperity may terminate the reorganization agreement if Legacy or the Legacy board of directors has made a change in recommendation or failed to comply in any material respect with its obligations described under “—Legacy Stockholder Meeting and Recommendation of Legacy Board of Directors” or “—No Negotiation with Others.”

Termination Fee (page 122)

Legacy will pay Prosperity an $82 million termination fee if the reorganization agreement is terminated in the following circumstances:

Amendment or Waiver of the Reorganization Agreement (page 123)

Prosperity and Legacy may amend the reorganization agreement and each party may waive its right to require the other party to adhere to any term or satisfy any condition of the reorganization agreement in accordance with the terms of the reorganization agreement. However, after approval of the reorganization agreement by the Legacy stockholders or the Prosperity shareholders, there may not be any amendment that requires further approval of such stockholders or shareholders under applicable law without obtaining such approval.

Material U.S. Federal Income Tax Consequences of the Merger (page 63)125)

The merger is intended to qualify as a reorganization under“reorganization” within the meaning of Section 368(a) of the Code, and it is a condition to the respective obligations of Prosperity and TraditionLegacy to complete the merger that each of Prosperity and Tradition receiveLegacy receives a legal opinion from their respective counselto that the merger qualifies as a reorganization.effect. Consistent with such treatment, as a result of receiving Prosperity common stock and cash in exchange for Tradition common stock, in general, a U.S. holder (as defined in the section titled “—Material U.S. Federal Income Tax Consequences of the Merger” beginning on page 63)125) of TraditionLegacy common stock will recognize any gain, but will not be permitted to recognize loss, for U.S. federal income tax purposes on the exchange of shares of Legacy common stock for shares of Prosperity common stock in the merger, in an amount equal to the lesser of (a) the cash consideration received (excluding cash received orin lieu of a fractional share) and (b) the gain realized in the merger.realized. The amount of gain realized by a U.S. holder will be equal to the amount by which the cash plus the fair market value, at the effective time of the merger, of the Prosperity common stock received exceeds the holder’s adjusted tax basis in Traditionthe Legacy common stock to be surrendered in exchange therefor.

This The tax treatment may not applyconsequences to every shareholdera U.S. holder of Tradition. DeterminingLegacy common stock will depend on his, her or its individual situation. Accordingly, we strongly urge holders of Legacy common stock to consult their tax advisors for a full understanding of the actualparticular tax consequences of the merger to them.

Accounting Treatment (page 124)

The merger will be accounted for as an acquisition of Legacy and Legacy Bank by Prosperity and Prosperity Bank under the acquisition method of accounting in accordance with the Financial Accounting Standard Board’s Accounting Standard Codification Topic 805,Business Combinations.

The Legacy Special Meeting (page 51)

The special meeting of stockholders of Legacy will be held on October 28, 2019, at 11:00 a.m. Central Time, at 5851 Legacy Circle, Plano, Texas 75024. At the Legacy special meeting, Legacy’s stockholders will be asked to consider and vote on the following:

You may vote on the proposals to come before the special meeting of Legacy stockholders if you owned shares of Legacy common stock of record as of the record date. You can cast one vote for each share of Legacy common stock that you owned of record at that time; provided, however, that Legacy’s articles of incorporation generally prohibit any stockholder who beneficially owns more than 10% of the outstanding shares of Legacy common stock from voting shares in excess of that amount. As of the record date, there were 49,156,231 shares of Legacy common stock outstanding.

At the close of business on the record date for the Legacy special meeting, Legacy directors and executive officers and their respective affiliates were entitled to vote approximately 973,397 shares of Legacy common stock, or approximately 2.0% of the shares of Legacy common stock outstanding on that date.

Legacy Proposals: Required Vote and Treatment of Abstentions and Failure to Vote (page 52)

The Legacy merger proposal requires the affirmative vote of the holders of a majority of the votes entitled to be cast at the Legacy special meeting. Failures to vote, broker nonvotes and abstentions will have the same effect as a vote against this proposal.

The Legacy compensation proposal requires the affirmative vote of a majority of votes cast by the Legacy stockholders entitled to vote on such proposal at the Legacy special meeting. Failures to vote, abstentions and broker nonvotes will have no effect on the proposal.

The Legacy adjournment proposal requires the affirmative vote of a majority of votes cast by the Legacy stockholders entitled to vote on such proposal at the Legacy special meeting. Failures to vote, abstentions and broker nonvotes will have no effect on the proposal.

A holder of Legacy common stock may be complicatedvote his or her shares of Legacy common stock by attending the special meeting and will dependvoting in person, by completing and mailing the enclosed proxy card, or by following the instructions to vote via the Internet or by telephone as indicated on the proxy card and elsewhere in this joint proxy statement/prospectus. If you are the record holder of such shares, you can revoke your proxy at any time before the vote is taken at the Legacy special meeting by sending a written notice revoking the proxy or submitting a later-dated proxy to the Corporate Secretary of Legacy; completing, signing and returning a new proxy card with a later date than the date on your specific situationoriginal proxy card, in which case any earlier proxy will be revoked automatically; or by logging onto the Internet website specified on your proxy card in the same manner you would to submit your proxy electronically or by calling the telephone number specified on your proxy card, in each case if you are eligible to do so, and following the instructions indicated on variables not within our control. We strongly recommend thatthe proxy card prior to 11:59 p.m. Central Time, on October 27, 2019. You may also revoke your proxy by voting in person at the Legacy special meeting. If your shares are held in “street name” and you consult your own tax advisor for a full understandingdesire to change any voting instructions you have previously given to the record holder of the tax consequencesshares of which you are the beneficial owner, you should contact the broker, bank, trustee or other nominee holding your shares in “street name” in order to direct a change in the manner your shares will be voted. See “The Legacy Special Meeting—Voting of Proxies by Holders of Record,” “—Attending the Meeting; Voting in Person” and “—Revocation of Proxies.”

The Prosperity Special Meeting (page 56)

The special meeting of shareholders of Prosperity will be held on October 29, 2019, at 10:30 a.m. Central Time, at 80 Sugar Creek Center Blvd., Sugar Land, Texas 77478. At the Prosperity special meeting, Prosperity’s shareholders will be asked to consider and vote on the following:

You may vote at the special meeting of Prosperity shareholders if you owned Prosperity common stock of record as of the record date. You can cast one vote for each share of Prosperity common stock you owned of record at that time. As of the record date, there were 68,396,778 shares of Prosperity common stock outstanding.

At the close of business on the record date for the Prosperity special meeting, Prosperity directors and executive officers and their respective affiliates were entitled to vote approximately 3,662,278 shares of Prosperity common stock, or approximately 5.4% of the shares of Prosperity common stock outstanding on that date.

Prosperity Proposals: Required Vote and Treatment of Abstentions and Failure to Vote (page 57)

The required votes to approve the Prosperity proposals are as follows:

The Prosperity merger proposal requires the affirmative vote of the holders of at least a majority of the issued and outstanding shares of Prosperity common stock entitled to vote at the Prosperity special meeting. Failures to vote, broker nonvotes and abstentions will have the same effect as a vote against this proposal.

The Prosperity adjournment proposal requires the affirmative vote of a majority of votes cast by the Prosperity shareholders entitled to vote on such proposal at the Prosperity special meeting. Failures to vote, broker nonvotes and abstentions will have no effect on the vote for the proposal.

You may vote your shares of Prosperity common stock by attending the special meeting and voting in person, by completing and mailing the enclosed proxy card or by following the instructions to vote via the Internet or by telephone as indicated on the proxy card and elsewhere in this joint proxy statement/prospectus. If you are the record holder of your shares, you can revoke your proxy at any time before the vote is taken at the Prosperity special meeting by sending a written notice revoking the proxy or submitting a later dated proxy to the Corporate Secretary of Prosperity, which must be received no later than immediately prior to the vote at the Prosperity special meeting, or by logging onto the Internet website specified on your proxy card in the same manner you would to submit your proxy electronically or by calling the telephone number specified on your proxy card, in each case if you are eligible to do so, and following the instructions indicated on the proxy card prior to 11:59 p.m. Central Time, on October 28, 2019. You may also revoke your proxy by voting in person at the Prosperity special meeting. If your shares of Prosperity common stock are held in “street name” and you desire to change any voting instructions you have previously given to the record holder of the shares of which you are the beneficial owner, you should contact the broker, bank, trustee or other nominee holding your shares in “street name” in order to direct a change in the manner your shares will be voted. See “The Prosperity Special Meeting—Voting of Proxies by Holders of Record,” “—Attending the Meeting; Voting in Person” and “—Revocation of Proxies.”

Comparison of Rights of Stockholders of Legacy and Shareholders of Prosperity (page 137)

Legacy is a Maryland corporation that is a registered bank holding company, and the rights of stockholders of Legacy are governed by Maryland law and Legacy’s articles of incorporation and bylaws. Prosperity is a Texas corporation that is a registered financial holding company, and the rights of Prosperity’s shareholders are governed by Texas law and Prosperity’s articles of incorporation and bylaws. Upon completion of the merger, Legacy stockholders will become shareholders of Prosperity and their rights as shareholders of Prosperity will be governed by Prosperity’s articles of incorporation and bylaws, in addition to you.

Texas law. Prosperity’s articles of incorporation and bylaws will not be amended in the merger, but could be later restated, amended or, with respect to the bylaws, repealed.

OpinionSELECTED HISTORICAL CONSOLIDATED FINANCIAL INFORMATION OF PROSPERITY

The following selected historical consolidated financial information of Prosperity as of and for the six months ended June 30, 2019 and 2018 has been derived from Prosperity’s unaudited consolidated financial statements incorporated by reference in this joint proxy statement/prospectus and, in the opinion of Prosperity’s management, includes all normal and recurring adjustments that are considered necessary for the fair presentation of the results for those interim periods. The following selected consolidated financial information of Prosperity as of December 31, 2018 and 2017 and for the years ended December 31, 2018, 2017 and 2016 has been derived from Prosperity’s audited consolidated financial statements incorporated by reference in this joint proxy statement/prospectus, and the selected consolidated financial information as of December 31, 2016, 2015 and 2014 and for the years ended December 31, 2015 and 2014, has been derived from Prosperity’s audited consolidated financial statements not appearing or incorporated by reference in this joint proxy statement/prospectus.

You should read the following financial information relating to Prosperity in conjunction with other information contained in this joint proxy statement/prospectus, including consolidated financial statements of Prosperity and related accompanying notes appearing in Prosperity’s Annual Report on Form10-K most recently filed with the SEC and in the Quarterly Reports on Form10-Q of Prosperity filed with the SEC after that Annual Report on Form10-K was filed, and in any Current Report on Form8-K of Prosperity containing consolidated financial statements of Prosperity that was filed with the SEC after such Annual Report on Form10-K, each of which reports is incorporated by reference in this joint proxy statement/prospectus. Prosperity’s historical results for any prior period are not necessarily indicative of results to be expected in any future period, and Prosperity’s historical results for the six months ended June 30, 2019 are not necessarily indicative of its results to be expected for all of 2019. Prosperity has consummated several acquisitions during certain of the fiscal periods below. The results and other financial information of those acquired operations are not included in the table below for the periods or dates prior to their respective acquisition dates and, therefore, the results for such prior periods are not comparable in all respects. In addition, the selected financial information in the table immediately below does not include, on any basis, the results or financial condition of Legacy for any period or as of any date.

SELECTED HISTORICAL CONSOLIDATED FINANCIAL INFORMATION OF LEGACY

The following selected historical consolidated financial information of Legacy as of and for the six months ended June 30, 2019 and 2018 has been derived from Legacy’s unaudited consolidated financial statements as of and for the six months ended June 30, 2019 and 2018 incorporated by reference in this joint proxy statement/prospectus and, in the opinion of Legacy’s management, includes all normal and recurring adjustments that are considered necessary for the fair presentation of the results for those interim periods. The following selected consolidated financial information of Legacy as of and for the years ended December 31, 2018, 2017 and 2016 has been derived from Legacy’s audited consolidated financial statements incorporated by reference in this joint proxy statement/prospectus, and the selected consolidated financial information as of and for the years ended December 31, 2015 and 2014 has been derived from Legacy’s audited consolidated financial statements not appearing or incorporated by reference in this joint proxy statement/prospectus.

You should read the following financial information relating to Legacy in conjunction with other information contained in this joint proxy statement/prospectus or incorporated by reference, including the consolidated financial statements of Legacy and related accompanying notes appearing in Legacy’s Annual Report on Form10-K most recently filed with the SEC and in the Quarterly Reports on Form10-Q of Legacy filed with the SEC after that Annual Report on Form10-K was filed, and in any Current Report on Form8-K of Legacy containing consolidated financial statements of Legacy that was filed with the SEC after such Annual Report on Form10-K, each of which reports is incorporated by reference in this joint proxy statement/prospectus. Legacy’s historical results for any prior period are not necessarily indicative of results to be expected in any future period, and Legacy’s historical results for the six months ended June 30, 2019 are not necessarily indicative of its results to be expected for all of 2019. The results and other financial information of any acquired operations are not included in the table below for the periods or dates prior to their respective acquisition dates and, therefore, the results for these prior periods are not comparable in all respects.

Please see the section entitled “Where You Can Find More Information” for instructions on how to obtain the information that has been incorporated by reference. You should not assume the results of operations for past years indicate results for any future period.