Thomas J. Mancinelli serves as the Principal Deputy Assistant Secretary of Defense for Legislative Affairs. In this role, Tom advises the Secretary and Deputy Secretary on all matters pertaining to the Department of Defense’s relations with Congress, including the promotion of mutual understanding and cooperation between the Department of Defense and the Legislative Branch.

Prior to assuming his current position in April 2022, Tom was the National Security Advisor for Senator Chris Coons of Delaware, where he led the Senator’s work on the Foreign Relations Committee and the Appropriations Subcommittee that funds foreign assistance. Tom helped Senator Coons craft legislation to create the new U.S. international development finance agency, address the root causes of terrorism, invest in strategic competition with China, increase electricity access in Africa, and oversee the Iran nuclear deal.

From 2012 to 2014, Tom was the Chief of Staff in the State Department's Bureau of Political-Military Affairs. Earlier in his career, Tom also worked for former Deputy Secretary of State Thomas R. Nides, and in the National Security Division of the Office of Management and Budget.

Prior to serving in the federal government, Tom deployed twice to Iraq's Anbar province as a Marine. He has a master's degree from Georgetown's School of Foreign Service and a bachelor's from the United States Naval Academy, where he was awarded the Harry S. Truman Scholarship. Tom is the recipient of numerous civilian and military awards including the 2016 Ike Skelton Award for Public Service Leadership. Tom is a term member of the Council on Foreign Relations and a security fellow with the Truman National Security Project. He lives with his wife Sarah, his son George, and his daughter Ruth in Washington, DC.