Ms. Seileen Mullen is currently serving as the Acting Assistant Secretary of Defense for Health Affairs. Prior to her present role, she served as the Principal Deputy Assistant Secretary of Defense for Health Affairs from March 2023 to October 2024, and Performing the Duties of Assistant Secretary of Defense for Health Affairs from March 2022 to February 2023. In this role, she is the principal advisor to the Secretary of Defense and the Undersecretary of Defense for Personnel and Readiness for all Department of Defense health and force health protection policies, programs, and activities.

Mullen has spent nearly 30 years in or around military health. Prior to being named the Acting Assistant Secretary of Defense for Health Affairs in 2022, she served as the Chief Operating Officer of Martin, Blanck & Associates, a health care policy firm, with a focus in military health. She became Chief Operating Officer in January 2007, and was responsible for day-to-day operations, including management of client relations, and internal communications and external partnerships. At Martin, Blanck & Associates, she worked extensively military health issues, including on matters relating to both the Direct Care and Purchased Care Systems.

Mullen graduated with a Bachelor of Arts from the University of Virginia in 1984. From 1985 to 1993, she served in the House of Representatives in a variety of roles. She spent three years as a professional staff member on the House Armed Services Committee.

In February 1993, she joined the Department of Defense. From 1994 to 1996, she served as the Special Assistant and Executive Officer to the Assistant Secretary of Defense for Health Affairs, where she provided advice and counsel to the Assistant Secretary of Defense for Health Affairs on health care and operational policy matters. In this role, she also contributed to the publication of the Final Report of the White House Task Force on Persian Gulf War.

From 1996 to 1998, Mullen was the Director of the Department of Defense's TRICARE Management Activity's Aurora Field Office. In this role as the Head of Contracting Activity, she managed TRICARE's contracting activities, as well as approximately 350 personnel in TRICARE's Colorado and Washington, D.C. contracting offices.

From 1999 to 2001, Mullen served as the Director of Federal Government Relations for the Salt Lake Organizing Committee for the Olympic Winter Games of 2002. She worked daily with the White House Task Force for the Olympics in securing appropriations for the 2002 Olympic Games and all aspects of government relations at the federal and state level. From 2001 to 2004, she provided program consulting services to the TRICARE Management Activity in support of the TRICARE Next Generation contracts for managed care services, which represented $32 billion in federal healthcare contracting.

She served as a member of the Virginia Medical Reserve Corps during the COVID-19 pandemic. She is a recipient of the Department of Defense Outstanding Public Service Award.