Byline Bancorp, Inc.

Item 5.02 Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; Compensatory Arrangements of Certain Officers. On October 08, 2026, Byline Bancorp, Inc. (the “Company”) and its wholly-owned subsidiary Byline Bank (the “Bank”) announced the following leadership changes, which will become effective January 1, 2027: Retirement of Brogan M. Ptacin, Head of Commercial Banking On October 08, 2026, Brogan Ptacin, Executive Vice President and Head of Commercial Banking, and a named executive officer of the Company, provided notice of his decision to retire from his position effective December 31, 2026. Following his retirement, Mr. Ptacin will be employed by the Bank in a non-executive, part-time, advisory capacity for a period of time to be determined. Appointment of Sean H. McGuire as Chief Commercial Banking Officer On October 08, 2026, the Bank appointed Sean H. McGuire, age 58, to the newly created positon of Chief Commercial Banking Officer, to be effective January 1, 2027. Mr. McGuire joined the Bank in July 2019 and currently serves as Commercial Banking Group Head. Prior to his role at the Bank, Mr. McGuire served as Commercial Group President at MB Financial Bank from August 2009 until July 2019. Prior to his role at MB Financial Bank, Mr. McGuire served as a Senior Vice President at Fifth Third Bank. Mr. McGuire received a Bachelor’s degree in Economics from the University of Notre Dame and a Masters of Business Administration from the Quinlan School of Business, Loyola University, Chicago. Retirement of Mark Fucinato, Chief Credit Officer On October 08, 2026, Mark Fucinato, Executive Vice President and Chief Credit Officer, provided notice of his decision to retire from his position effective December 31, 2026. Following his retirement, Mr. Fucinato will be employed by the Bank in a non-executive, part-time, advisory capacity for a period of time to be determined. On October 08, 2026, the Company and the Bank appointed Scott Hawthorne, age 46, to succeed Mr. Fucinato as Chief Credit Officer, to be effective January 1, 2027. Mr. Hawthorne joined the Bank in June 2023 and currently serves as Deputy Chief Credit Officer. Prior to his role at the Bank, Mr. Hawthorne served in several senior credit and credit risk roles at Fifth Third Bank from May 2019 to June 2023 and at MB Financial Bank from May 2005 to May 2019.

Item 7.01 Regulation FD Disclosure. There are no family relationships between Messrs. McGuire or Hawthorne and any director or executive officer of the Company or the Bank, nor any arrangement or understanding between Mr. McGuire or Mr. Hawthorne and any other person pursuant to which he was appointed as an officer of the Company and/or the Bank. Also, neither Mr. McGuire nor Mr. Hawthorne has a direct or indirect material interest in any transaction that would be required to be reported under Item 404(a) of Regulation S-K. A copy of the Company’s press release announcing these leadership changes is attached as Exhibit 99.1and incorporated herein by reference.