Exhibit 99.1

FOR IMMEDIATE RELEASE

PROSPERITY BANCSHARES, INC.^®

REPORTS FIRST QUARTER

2020 EARNINGS

HOUSTON, April 29, 2020. Prosperity Bancshares, Inc.^® (NYSE: PB), the parent company of Prosperity Bank^® (collectively, “Prosperity”), reported net income for the quarter ended March 31, 2020 of $130.848 million compared with $82.402 million for the same period in 2019. Net income per diluted common share was $1.39 compared with $1.18 for the same period in 2019. Additionally, loans increased 1.5% during the first quarter 2020 and nonperforming assets remain low at 0.25% of first quarter average interest-earning assets. On November 1, 2019, LegacyTexas Financial Group, Inc. (“LegacyTexas”), merged with Prosperity Bancshares and LegacyTexas Bank merged with Prosperity Bank (collectively, the “Merger”).

“I am proud to announce that Prosperity posted diluted earnings per share of $1.39 for the first quarter of 2020, a 17.8% increase compared with the same period in 2019. Our merger with LegacyTexas was completed on November 1, 2019 and our management teams continue to find commonalties and strengths that we expect will benefit our company, shareholders and associates going forward.  Our planned operational integration remains on schedule for June of this year,” said David Zalman, Prosperity’s Senior Chairman and Chief Executive Officer.

“In our efforts to continue enhance shareholder value, during the first quarter 2020 Prosperity repurchased 2.092 million shares of its common stock at a weighted average price of $52.59 per share,” continued Zalman.

“Also, during the first quarter of 2020, Prosperity increased its allowance for credit losses on loans to $327.206 million from $87.469 million for the fourth quarter of 2019 after adopting accounting standard ASU 2016-13, also known as CECL. The amount of the allowance is based on our CECL methodology. We believe that these additional reserves should help insulate the company during these challenging and unprecedented times. Our allowance for credit losses to total loans, excluding warehouse purchase program loans, now stands at 1.88% compared to 0.51% at December 31, 2019,” added Zalman.

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“While today’s challenges are certainly extraordinary, Prosperity has a deep management team with experience navigating and adapting to difficult times. We entered this economic downturn from a position of strength, with sound credit quality, robust capital and liquidity and solid operating fundamentals. We believe that our team will see us through and we remain confident in our long-term future,” stated Zalman.

“I would like to thank every associate at Prosperity. Throughout the past several months, while dealing with various personal challenges related to the pandemic, our retail team operated at full capacity, enabling us to keep our locations open and serve our customers’ daily needs. Additionally, our operational staff and lending team were crucial in accepting, processing and submitting thousands of SBA PPP applications and closing the loans, working around the clock to assist our customers,” concluded Zalman.

Results of Operations for the Three Months Ended March 31, 2020

Net income was $130.848 million⁽²⁾ for the three months ended March 31, 2020 compared with $82.402 million⁽³⁾ for the same period in 2019. Net income per diluted common share was $1.39 for the three months ended March 31, 2020 compared with $1.18 for the same period in 2019. Annualized returns on average assets, average common equity and average tangible common equity for the three months ended March 31, 2020 were 1.67%, 8.86% and 20.16%⁽¹⁾, respectively. Prosperity’s efficiency ratio (excluding net gains on the sale of assets and taxes) was 42.90%⁽¹⁾ for the three months ended March 31, 2020. Excluding merger related expenses of $544 thousand, net of tax, the efficiency ratio was 42.71%⁽¹⁾ for the three months ended March 31, 2020.

Net interest income before provision for credit losses for the three months ended March 31, 2020 was $256.031 million compared with $154.911 million for the same period in 2019, an increase of $101.120 million or 65.3%. The increase was primarily due to the Merger and the increase in loan discount accretion of $26.689 million. On a linked quarter basis, net interest income before provision for credit losses was $256.031 million compared with $232.030 million for the three months ended December 31, 2019. The increase was primarily due to the increase in loan discount accretion of $4.740 million and three months of combined bank earnings in the first quarter of 2020 compared with only two months in the fourth quarter 2019.

The net interest margin on a tax equivalent basis was 3.81% for the three months ended March 31, 2020 compared with 3.20% for the same period in 2019. The change was primarily due to increased interest-earning assets and the $26.689 million increase in loan discount accretion. On a linked quarter basis, the net interest margin on a tax equivalent basis was 3.81% for the three months ended March 31, 2020 compared with 3.66% for the three months ended December 31, 2019. The change was primarily due to increased interest-earning assets and the $4.740 million increase in loan discount accretion.

Noninterest income was $34.388 million for the three months ended March 31, 2020 compared with $28.144 million for the same period in 2019, an increase of $6.244 million or 22.2%. This increase was primarily due to an increase in nonsufficient funds fees, credit card, debit card and ATM card fees, mortgage income, service fees and other noninterest income primarily due to the Merger. On a linked quarter basis, noninterest income decreased $1.118 million or 3.1% to $34.388 million compared with $35.506 million for the three months ended December 31, 2019, primarily due to the decrease in other noninterest income and mortgage income, partially offset by lower net loss on write-down of assets.

Noninterest expense was $124.741 million for the three months ended March 31, 2020 compared with $78.571 million for the same period in 2019, an increase of $46.170 million or 58.8%, primarily due to the Merger. On a linked quarter basis, noninterest expense decreased $31.710 million or 20.3% to $124.741 million compared with $156.451 million for the three months ended December 31, 2019. The decrease was primarily due to the decrease of merger related expenses partially offset by increases in salaries and benefits, credit and debit card, data processing and software amortization, and net occupancy and equipment due to three months of combined bank noninterest expenses in the first quarter 2020 compared with two months in fourth quarter 2019.

Balance Sheet Information

At March 31, 2020, Prosperity had $31.743 billion in total assets, an increase of $9.389 billion or 42.0%, compared with $22.354 billion at March 31, 2019.

Loans at March 31, 2020 were $19.127 billion, an increase of $8.713 billion or 83.7%, compared with $10.414 billion at March 31, 2019. Linked quarter loans increased $281.849 million or 1.5% from $18.845 billion at December 31, 2019.

As part of its lending activities, Prosperity extends credit to oil and gas production and servicing companies. Oil and gas production loans are loans to companies directly involved in the exploration and or production of oil and gas. Oil and gas servicing loans are loans to companies that provide services for oil and gas production and exploration. At March 31, 2020, oil and gas loans totaled $718.654 million (net of discount) or 3.8% of total loans, of which $435.041 million were production

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loans and $283.613 million were servicing loans, compared with total oil and gas loans of $380.835 million (net of discount) or 3.7% of total loans at March 31, 2019, of which $115.571 million were production loans and $265.264 million were servicing loans. In addition, as of March 31, 2020, Prosperity had total unfunded commitments to oil and gas companies of $389.515 million compared with total unfunded commitments to oil and gas companies of $231.474 million as of March 31, 2019. Unfunded commitments to producers include letters of credit issued in lieu of oil well plugging bonds.

Additionally, Prosperity extends credit to hotels and restaurants.  At March 31, 2020, loans to hotels totaled $374.105 million or 2.0% of total loans and loans to restaurants totaled $204.600 million or 1.1% of total loans.

Deposits at March 31, 2020 were $23.826 billion, an increase of $6.628 billion or 38.5%, compared with $17.198 billion at March 31, 2019. Linked quarter deposits decreased $373.375 million or 1.5% from $24.200 billion at December 31, 2019.

The table below provides detail on the impact of loans acquired and deposits assumed in the Merger:

Excluding loans acquired in the Merger and new production by the acquired lending operations since November 1, 2019, loans at March 31, 2020 grew $231.845 million or 2.2% compared with March 31, 2019 and grew $56.883 million or 0.5% compared with December 31, 2019.

Excluding deposits assumed in the Merger and new deposits generated at the acquired banking centers since November 1, 2019, deposits at March 31, 2020 grew $1.023 billion or 6.0% compared with March 31, 2019 and grew $162.185 million or 0.9% compared with December 31, 2019.

Asset Quality

Nonperforming assets totaled $67.179 million or 0.25% of quarterly average interest-earning assets at March 31, 2020, compared with $40.883 million or 0.21% of quarterly average interest-earning assets at March 31, 2019, and $62.943 million or 0.25% of quarterly average interest-earning assets at December 31, 2019.

The allowance for credit losses on loans was $327.206 million or 1.71% of total loans at March 31, 2020 compared to $87.469 million or 0.46% of total loans at December 31, 2019 and $86.091 million or 0.83% of total loans at March 31, 2019.  On January 1, 2020, Prosperity adopted the measurement of current expected credit losses (“CECL”). Upon adoption of CECL, Prosperity recognized an increase in allowance for credit losses on loans of $108.698 million, of which $102.545 million was related to LegacyTexas and an increase in allowance for credit losses on off-balance sheet credit exposures of $24.443 million, of which $6.314 million was related to LegacyTexas, with a corresponding decrease in retained earnings (pre-tax). Additionally, Prosperity recognized an increase in the allowance for credit losses on loans of $131.841 million, of which $130.278 million was related to LegacyTexas, due to the reclass of purchased credit deteriorated (“PCD”) discounts as a result of adopting CECL.

Prosperity had a $13.150 million provision for credit losses reflecting forecasted credit deterioration due to the COVID-19 pandemic for the first quarter of 2020. Countering this provision, during the first quarter of 2020, several purchase credit deteriorated (“PCD”) loans were repaid in full, which cleared $8.576 million in specific reserves. Additionally, balance changes and historical loss rate improvements released $5.471 million in general reserves. Combined, these events fully offset the provision. Accordingly, there was

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no provision for credit losses for the three months ended March 31, 2020 compared with $700 thousand for the three months ended March 31, 2019 and $1.700 million for the three months ended December 31, 2019.  

Net charge-offs were $801 thousand for the three months ended March 31, 2020 compared with net charge-offs of $1.049 million for the three months ended March 31, 2019 and net charge-offs of $1.291 million for the three months ended December 31, 2019.

Dividend

Prosperity Bancshares declared a second quarter cash dividend of $0.46 per share to be paid on July 1, 2020 to all shareholders of record as of June 15, 2020.

Stock Repurchase Program

On January 29, 2020, Prosperity Bancshares announced a stock repurchase program under which up to 5%, or approximately

4.740 million shares, of its outstanding common stock may be acquired over a one-year period expiring on January 28, 2021, at the discretion of management. Prosperity Bancshares repurchased 2.092 million shares of its common stock at an average weighted price of $52.59 per share during the three months ended March 31, 2020.

COVID-19 Pandemic

In December 2019, a novel strain of coronavirus disease (“COVID-19”) was first reported in Wuhan, Hubei Province, China. On March 11, 2020, the World Health Organization declared COVID-19 a pandemic, and on March 13, the U.S. President announced a national emergency relating to the pandemic. On March 13, the Texas governor signed a proclamation certifying that COVID-19 poses an imminent threat of disaster in the state and declaring a state of disaster for all counties in Texas. Prosperity Bank (the “Bank”) is considered an essential business and is closely monitoring the latest developments regarding COVID-19. The health and safety of our associates, customers, and communities are of utmost importance, and the Bank remains committed to providing uninterrupted service. Additionally, the Bank has continuity plans in place to ensure critical operations are able to continue without disruption. The COVID-19 pandemic has resulted in significant economic uncertainties that could negatively impact Prosperity’s operating income, financial condition and cash flows.

Merger with LegacyTexas Financial Group, Inc.

On November 1, 2019, Prosperity completed the merger with LegacyTexas and its wholly-owned subsidiary LegacyTexas Bank headquartered in Plano, Texas. LegacyTexas Bank operated 42 locations in 19 North Texas cities in and around the Dallas-Fort Worth area.  

Pursuant to the terms of the merger agreement, Prosperity issued 26,228,148 shares of Prosperity common stock with a closing price of $69.02 per share plus $318.018 million in cash, made up of $308.585 million in cash and $9.433 million in cash for taxes withheld, for all outstanding shares of LegacyTexas. This resulted in goodwill of $1.322 billion as of March 31, 2020, which was subject to subsequent fair value adjustments.

Conference Call

Prosperity’s management team will host a conference call on Wednesday, April 29, 2020 at 11:30 a.m. Eastern Time (10:30 a.m. Central Time) to discuss Prosperity’s first quarter 2020 earnings. Individuals and investment professionals may participate in the call by dialing 877-883-0383 for domestic participants, or 412-902-6506 for international participants. The elite entry number is 3056906.

Alternatively, individuals may listen to the live webcast of the presentation by visiting Prosperity’s website at www.prosperitybankusa.com. The webcast may be accessed from Prosperity’s home page by selecting “Presentations & Calls” from the drop-down menu on the Investor Relations tab and following the instructions.

Non-GAAP Financial Measures

Prosperity’s management uses certain non-GAAP financial measures to evaluate its performance. Specifically, Prosperity reviews tangible book value per share, return on average tangible common equity, tangible equity to tangible assets ratio and the efficiency ratio, excluding net gains and losses on the sale of assets and securities. Prosperity believes these non-GAAP financial measures provide information useful to investors in understanding Prosperity’s financial results and that their presentation, together with the accompanying reconciliations, provides a more complete understanding of factors and trends affecting Prosperity’s business and allows investors to view performance in a manner similar to management, the entire financial services sector, bank stock analysts and bank regulators. Further, Prosperity believes that these non-GAAP financial measures provide useful information by excluding certain items that may not be indicative of its core operating earnings and business outlook. These non-GAAP financial measures should not be considered a substitute for, nor of greater importance than, GAAP basis financial measures and results; Prosperity strongly encourages investors to review its consolidated financial statements in their entirety and not to rely on any single financial measure. Because non-GAAP financial measures are not standardized, it may not be possible to compare these financial measures with other companies’ non-GAAP financial measures having the same or similar names. Please refer to the “Notes to Selected Financial Data” at

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the end of this Earnings Release for a reconciliation of these non-GAAP financial measures to the nearest respective GAAP financial measures.

Prosperity Bancshares, Inc. ®

As of March 31, 2020, Prosperity Bancshares, Inc.^® is a $31.7 billion Houston, Texas based regional financial holding company providing personal banking services and investments to consumers and businesses throughout Texas and Oklahoma.  Founded in 1983, Prosperity believes in a community banking philosophy, taking care of customers, businesses and communities in the areas it serves by providing financial solutions to simplify everyday financial needs. In addition to offering traditional deposit and loan products, Prosperity offers digital banking solutions, credit and debit cards, mortgage services, retail brokerage services, trust and wealth management, and cash management.

As of March 31, 2020, Prosperity operated 285 full-service banking locations: 65 in the Houston area, including The Woodlands; 30 in the South Texas area including Corpus Christi and Victoria; 33 in the Dallas/Fort Worth area; 22 in the East Texas area; 29 in the Central Texas area including Austin and San Antonio; 34 in the West Texas area including Lubbock, Midland-Odessa and Abilene; 16 in the Bryan/College Station area; 6 in the Central Oklahoma area; 8 in the Tulsa, Oklahoma area and 42 in the Dallas/Fort Worth area currently doing business as LegacyTexas Bank.

Cautionary Notes on Forward-Looking Statements

“Safe Harbor” Statement under the Private Securities Litigation Reform Act of 1995: This release contains, and the remarks by Prosperity’s management on the conference call may contain, forward-looking statements within the meaning of the federal securities laws, including Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended. Forward-looking statements are typically, but not exclusively, identified by the use in the statements of words or phrases such as “aim,” “anticipate,” “estimate,” “expect,” “goal,” “guidance,” “intend,” “is anticipated,” “is expected,” “is intended,” “objective,” “plan,” “projected,” “projection,” “will affect,” “will be,” “will continue,” “will decrease,” “will grow,” “will impact,” “will increase,” “will incur,” “will reduce,” “will remain,” “will result,” “would be,” variations of such words or phrases (including where the word “could,” “may,” or “would” is used rather than the word “will” in a phrase) and similar words and phrases indicating that the statement addresses some future result, occurrence, plan or objective. Forward-looking statements include all statements other than statements of historical fact, including forecasts or trends, and are based on current expectations, assumptions, estimates and projections about Prosperity Bancshares and its subsidiaries. These forward-looking statements may include information about Prosperity’s possible or assumed future economic performance or future results of operations, including future revenues, income, expenses, provision for loan losses, provision for taxes, effective tax rate, earnings per share and cash flows and Prosperity’s future capital expenditures and dividends, future financial condition and changes therein, including changes in Prosperity’s loan portfolio and allowance for loan losses, future capital structure or changes therein, as well as the plans and objectives of management for Prosperity’s future operations, future or proposed acquisitions, the future or expected effect of acquisitions on Prosperity’s operations, results of operations, financial condition, and future economic performance, statements about the anticipated benefits of the proposed transaction, and statements about the assumptions underlying any such statement, as well as expectations regarding the effects of the COVID-19 pandemic on the Bank’s operating income, financial condition and cash flows.  These forward‑looking statements are not guarantees of future performance and are subject to risks and uncertainties, many of which are outside of Prosperity’s control, which may cause actual results to differ materially from those expressed or implied by the forward-looking statements.  These risks and uncertainties include but are not limited to whether Prosperity can: successfully identify acquisition targets and integrate the businesses of acquired companies and banks, including LegacyTexas; continue to sustain its current internal growth rate or total growth rate; provide products and services that appeal to its customers; continue to have access to debt and equity capital markets; and achieve its sales objectives.  Other risks include, but are not limited to: the possibility that credit quality could deteriorate; actions of competitors; changes in laws and regulations (including changes in governmental interpretations of regulations and changes in accounting standards); the possibility that the anticipated benefits of an acquisition transaction, including the LegacyTexas transaction, are not realized when expected or at all, including as a result of the impact of, or problems arising from, the integration of two companies or as a result of the strength of the economy and competitive factors generally; a deterioration or downgrade in the credit quality and credit agency ratings of the securities in Prosperity’s securities portfolio; customer and consumer demand, including customer and consumer response to marketing; effectiveness of spending, investments or programs; fluctuations in the cost and availability of supply chain resources; economic conditions, including currency rate, interest rate and commodity price fluctuations; the effect, impact potential duration or other implications of the COVID-19 pandemic; and weather.  These and various other factors are discussed in Prosperity Bancshares’ Annual Report on Form 10-K for the year ended December 31, 2019 and other reports and statements Prosperity Bancshares has filed with the Securities and Exchange Commission (“SEC”). Copies of the SEC filings for Prosperity Bancshares may be downloaded from the Internet at no charge from http://www.prosperitybankusa.com.

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Prosperity Bancshares, Inc.^®

Financial Highlights (Unaudited)

(In thousands)

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Prosperity Bancshares, Inc.^®

Financial Highlights (Unaudited)

(In thousands)

(D) Interest income on securities was reduced by net premium amortization of $8,005, $8,556, $8,027, $7,607 and $6,589 for the three-month periods ended March 31, 2020, December 31, 2019, September 30, 2019, June 30, 2019 and March 31, 2019, respectively.

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Prosperity Bancshares, Inc. ^®

Financial Highlights (Unaudited)

(Dollars and share amounts in thousands, except per share data and market prices)

(E) Includes purchase accounting adjustments for the periods presented as follows:

(F) Using effective tax rate of 21.0%, 21.3%, 20.5%, 20.3% and 20.6% for the three-month periods ended March 31, 2020, December 31, 2019, September 30, 2019, June 30, 2019 and March 31, 2019, respectively.

(G) Interim periods annualized.

(H) Refer to the "Notes to Selected Financial Data" at the end of this Earnings Release for a reconciliation of this non-GAAP financial measure to the nearest GAAP financial measure.

(I) Net interest margin for all periods presented is based on average balances on an actual 365 day or 366 days basis.

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Prosperity Bancshares, Inc.^®

Financial Highlights (Unaudited)

(Dollars in thousands)