S&T BANCORP INC

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A

INFORMATION

Proxy Statement Pursuant to Section 14(a) of the

Securities Exchange Act of 1934

(Amendment No.

)

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To my fellow shareholders: S&T Bank was founded in 1902 on a simple but enduring belief: banking should begin and end with people. As we embark on 125 years, that principle continues to shape how we serve our customers, invest in our communities and create long-term value for our shareholders through our people-forward approach to banking. Our strategic framework, Our Shared Future, remains the foundation for disciplined execution and sustainable performance. It clarifies our purpose, sharpens our priorities and aligns our teams around profitable growth, prudent risk management and operational excellence. In 2025, we continued to turn strategy into measurable progress, strengthening our organization while positioning the Bank for sustained success in the years ahead.

2025 Performance and Strategic Progress

Throughout 2025, we advanced our key business drivers with focus and consistency. We delivered solid return metrics with return on tangible equity (non-GAAP) of 12.62% and return on assets of 1.38%. These returns were supported by total loan growth of $329 million and $220.5 million of customer deposit growth (total deposit growth of $175.7 million). S&T serves 132,000 households in Pennsylvania and Ohio with over 1,200 team members at more than 70 locations, reflecting intentional growth and expansion since our founding in Indiana, Pennsylvania. Importantly, our progress continues to be relationship-driven and supported by ongoing improvement in asset quality, strong capital levels and consistent growth in our customer deposit franchise.

A Culture That Delivers Results

At S&T, our culture is not just aspirational language; it is a true competitive advantage and woven into the fabric of who we are. Our team members bring our people-forward purpose to life by building trust, strengthening relationships and delivering thoughtful financial solutions. We are guided by our values, which define how we operate every day and turn purpose into action and strategy into meaningful results:

Our investment in our people is a strategic driver of our long-term success and enables our employees to deliver meaningful results for our customers, shareholders and communities. The external recognition we received in 2025 reflects the strength of that culture and underscores its impact across our organization.

The Bank has earned the following recognitions, to name a few:

These awards affirm that when we invest in our people, performance follows.

Community Impact

We believe financial performance and community impact are mutually reinforcing. In 2025, our employees once again demonstrated extraordinary commitment to the communities we serve.

Through employee giving campaigns and corporate philanthropy, S&T contributed:

Additionally, we provided $26.6 million in community development loans to support affordable housing initiatives, small business growth and revitalization efforts across our footprint.

These investments reflect our belief that strong communities create stronger economies and a stronger Bank.

Financial Highlights

The strength of our culture, combined with disciplined execution, produced solid financial results in 2025.

Financial highlights for the year include**:

Our performance also earned notable external recognition in 2025. S&T was named as one of Forbes* America’s Best Banks in 2025 for the third consecutive year, ranking 36 on the list and the highest-ranked bank headquartered in Pennsylvania. This is reflective of the strength of our profitability, capital, asset quality and shareholder returns as well as a meaningful validation of the Bank’s consistency and discipline behind its strategy and the collective drive and shared sense of purpose of its employees.

Positioning for the Future

The financial services industry continues to evolve, shaped by technological advancement, shifting customer expectations and a dynamic economic environment. We are investing strategically in digital capabilities, technology, talent development and our security and risk infrastructure to ensure we remain competitive and responsive.

While markets change, our foundation and people-forward banking purpose does not. We remain committed to disciplined growth, strong credit quality, capital strength and prudent expense management. Most importantly, we remain committed to earning the trust placed in us and building on Our Shared Future.

Christopher McComish

Chair and CEO

Lead Independent Director Letter to Shareholders Dear Shareholders, It is a privilege to write to you for the first time in my role as Lead Independent Director of S&T Bancorp, Inc. I am grateful for the confidence my fellow directors have placed in me and honored to serve our shareholders in this capacity. In late 2025, following the resignation of long-serving Chair Christine J. Toretti, who became an Ambassador to Sweden, the board appointed our Chief Executive Officer, Christopher J. McComish, to also serve as chair and established the role of lead independent director to strengthen independent oversight and effective governance. Maintaining a balanced and engaged board remains a priority. Our independent directors represent a broad range of professional backgrounds and experiences. Together, these perspectives enhance the board’s ability to engage constructively with management and provide thoughtful strategic guidance on behalf of our shareholders.

In October, we were pleased to welcome Stephanie N. Doliveira as a new independent director. Her experience at a large regional convenience retailer provides the board with deep expertise in culture and workforce strategy. In addition, her background in legal, regulatory and enterprise risk matters brings valuable perspective as the board continues to oversee the Bank’s strategy, risk framework and long-term planning.

S&T’s board structure provides unified leadership while maintaining a clear framework for strong independent oversight. As lead independent director, I work closely with the chair and my fellow independent directors to ensure the board maintains an independent perspective in its deliberations and effectively fulfills its oversight responsibilities.

The board recognizes that its role is distinct from that of senior management. While management leads the Bank’s day-to-day operations, the board provides strategic oversight and guidance by fostering open and constructive dialogue, challenging management when appropriate and helping position the Bank for long-term success. Our discussions regularly address financial performance, geopolitical developments, the evolving regulatory environment and emerging technologies such as artificial intelligence. Key matters, including liquidity, capital strength, cybersecurity, risk management and the broader economic landscape, are reviewed consistently across board and committee meetings.

As a board, our work is guided by the same people-forward purpose and values that define the Bank and shape how it serves customers, supports employees and strengthens the communities in which it operates.

The board also oversees the execution of the Bank’s strategic framework, Our Shared Future, which emphasizes deepening customer relationships, investing in people and capabilities, and pursuing disciplined, sustainable growth. Through ongoing engagement and the work of our board committees, we oversee the development and execution of the Bank’s strategy and help ensure management’s actions remain aligned with the Bank’s long-term objectives and the interests of our shareholders.

Our board remains committed to strong governance, active engagement and supporting the lasting success of the Bank. The Bank is well-positioned to advance its strategic priorities while delivering lasting value for all stakeholders.

On behalf of the entire board of directors, thank you for your continued support and confidence in S&T Bancorp, Inc. and S&T Bank. We appreciate your investment and remain focused on serving the best interests of our customers, colleagues, communities and shareholders.

Sincerely,

Jeffrey Grube

Lead Independent Director

Board of Directors

DATE AND TIME May 12, 2026, 10:00 a.m. Eastern Time via virtual online meeting only (www.virtualshareholdermeeting.com/STBA2026)

HOW TO VOTE

By Telephone Call (1-800-690-6903)

By Internet Visit www.proxyvote.com

By Mail Sign, date and return proxy card

To the Shareholders of

S&T Bancorp, Inc.:

Notice is hereby given that the Annual Meeting of Shareholders (“Annual Meeting”) of S&T Bancorp, Inc. (“S&T” or the “Company”) will be held on May 12, 2026, at 10:00 a.m. Eastern Time, via virtual online meeting only (www.virtualshareholdermeeting.com/STBA2026) for considering and voting on the following matters:

Only shareholders of record at the close of business on February 27, 2026 are entitled to notice of and to vote at such meeting or any adjournment thereof.

To participate in the virtual Annual Meeting

atwww.virtualshareholdermeeting.com/STBA2026, you need to use the 16-digit control number included on your Notice of Internet Availability of Proxy Materials, on your proxy card or on the instructions that accompanied your proxy materials. We encourage you to allow ample time for online check-in, which will begin at 9:30 a.m. Eastern Time. Please note that there is noin-person annual meeting for you to attend.

By Order of the Board of Directors,

Rachel L. Smydo

Secretary

Indiana, Pennsylvania

March 30, 2026

IMPORTANT

YOUR VOTE IS IMPORTANT, AND WE APPRECIATE YOUR TAKING THE TIME TO VOTE PROMPTLY USING ONE OF THE VOTING METHODS DESCRIBED IN THE PROXY STATEMENT.

THE BOARD OF DIRECTORS UNANIMOUSLY RECOMMENDS THAT THE SHAREHOLDERS VOTE FOR THE ELECTION AS DIRECTORS OF ALL OF THE NOMINEES NAMED IN THIS PROXY STATEMENT, FOR THE RATIFICATION OF THE SELECTION OF ERNST & YOUNG LLP AS S&T’S INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM FOR FISCAL YEAR 2026, AND FOR THE APPROVAL OF THE COMPENSATION OF S&T’S NAMED EXECUTIVE OFFICERS.

IMPORTANT NOTICE REGARDING THE AVAILABILITY OF

PROXY MATERIALS FOR THE 2026 ANNUAL MEETING OF SHAREHOLDERS

TO BE HELD ON MAY 12, 2026: OUR PROXY STATEMENT, 2025 ANNUAL REPORT AND NOTICE OF

ANNUAL MEETING OF SHAREHOLDERS ARE AVAILABLE ATWWW.PROXYVOTE.COM

We are taking advantage of a rule of the Securities and Exchange Commission (the “SEC”) which allows companies to make proxy materials available on a public website rather than in paper form. This rule allows a company to send some or all of its shareholders a Notice of Internet Availability of Proxy Materials (“Notice”) in place of the complete proxy package. For our 2026 Annual Meeting, to save significant printing and mailing expenses, S&T mailed a Notice to certain shareholders who had not previously elected to receive their proxy materials through the mail on or about March 30, 2026, to inform them of the electronic availability of the proxy materials 40 days in advance of the Annual Meeting.