Tom Mancinelli is a nonresident senior fellow in the GeoStrategy Initiative in the Atlantic Council’s Scowcroft Center for Strategy and Security. He is currently the head of federal strategy and policy at Antares, a Los Angeles-based defense technology start-up building kilowatt-scale nuclear fission reactors for national security applications on Earth and in space.  

Prior to Antares, Mancinelli served as acting under secretary of the Navy, where he oversaw the development of the $250 billion annual budget of the US Navy and Marine Corps. In this role, Mancinelli also managed over 850,000 personnel, including active duty and reserve sailors and marines as well as civilians. During this time, Mancinelli also led the Navy’s support of the Australia-United Kingdom-United States (AUKUS) trilateral security partnership, Department of Defense build-up on Guam, and efforts to improve US naval shipbuilding.

From April 2022 to July 2024, Mancinelli served as principal deputy assistant secretary of defense for legislative affairs, advising former Secretary of Defense Lloyd Austin and former Deputy Secretary of Defense Kathleen Hicks on all matters pertaining to the Pentagon’s relationship with Congress including legislation related to deterring China, supporting Ukraine, revitalizing the US defense industrial base, and quality of life for military service-members.

Before serving at the Pentagon, Mancinelli served seven years as national security advisor to Senator Chris Coons (D-DE) supporting the senator’s work on the Senate Foreign Relations Committee and the Appropriations Subcommittee that funds the State Department and foreign assistance.

Earlier in his career, Mancinelli served as chief of staff in the State Department’s Bureau of Political-Military Affairs. He was also a Presidential Management fellow, serving in rotational assignments on the staff of Deputy Secretary of State Tom Nides and on the staff of the National Security Division in the Office of Management and Budget.

Mancinelli served two tours of duty in 2005 and 2007 in Iraq’s Anbar province as a marine.

Mancinelli is a graduate of the US Naval Academy, and he received his master’s degree from Georgetown University’s School of Foreign Service. He lives in Washington, DC, with his wife Sarah, who is an attorney, and his two children, George and Ruth.