Dr. Thomas M. Williams began Performing the Duties of Under Secretary of Defense for Policy from January 15, 2021 to January 20, 2021. Previously he was performing the duties of Deputy Under Secretary of Defense for Policy.

Previously, he served as the Principal Deputy Assistant Secretary of Defense for Strategy, Plans, and Capabilities in the Office of the Secretary of Defense (OSD). 

Dr. Williams returned to OSD following two years at the National Security Council.  There he served as Deputy Assistant to the President and Senior Director for European Affairs, and prior to that as Acting Senior Director for Defense Policy and Strategy. 

Previously, Dr. Williams worked in OSD as Senior Advisor to the Assistant Secretary of Defense for Strategy, Plans, and Capabilities.  During that time, he contributed to the National Defense Strategy, Nuclear Posture Review, Missile Defense Review, D-ISIS Task Force, and Contingency Planning Guidance. 

Prior to government, Dr. Williams worked at the Center for Naval Analyses’ Strategic Initiatives Group, as a Visiting Assistant Professor of Politics at Washington and Lee University, as Research Assistant to Zbigniew Brzezinski at the Center for Strategic and International Studies, and at The Cohen Group. 

Dr. Williams earned a doctorate in Political Science from Johns Hopkins University and a bachelors degree in Foreign Service from Georgetown University.