While continuing his legal practice, Thomas Moore also served as the first Superintendent of the Fairfax County Public Schools beginning in 1870.

The College of William and Mary later awarded him a Phi Beta Kappa key and honorary LLD, and he was active in the Phi Beta Kappa society in Washington, D.C.[7] A lifetime bachelor, Moore lived with his unmarried sisters in Fairfax City (or later Washington when a Congressman and Congress was in session) and served on the vestry of Truro Episcopal Church.

Voters in Alexandria, Fairfax and Prince William Counties elected Moore to the Virginia State Senate, where he served one term (1887-1890) in the part-time position, succeeding Elisha E.

In 1896 Moore was mentioned as a candidate for the U.S. Congress, but did not receive the party's nomination (fellow Democrat John Franklin Rixey being elected instead).

[13] Nonetheless, Moore and state senator C. O'Conor Goolrick (of Fredericksburg, Virginia and first elected in 1908) were considered mavericks, beyond organization control.

His close friend and political ally, Secretary of State Cordell Hull convinced Moore to join the "Brain Trust" of President Franklin D. Roosevelt, succeeding Professor Raymond Moley.

Moore handled some patronage in the state, and advised Roosevelt to help Governor James Hubert Price as well as Judge Floyd H. Roberts of Bristol, Virginia, whom Byrd's ally Senator Carter Glass found "personally offensive.

His two principal candidates were Moore and Sumner Welles, Assistant Secretary of State for Latin American Affairs (a close ally and favorite of the President).

In subsequent years (until his death in 1941), Moore worked on issues including legal questions, aviation, and arms control.

Gray Temple officiated at his funeral at Truro church, which was attended by Secretary of State Hull, Virginia's governor Price, White House representatives, four U.S.

Congressmen (S. Otis Bland, Thomas G. Burch, Colgate Darden, Howard W. Smith), many diplomats and neighbors (including pallbearers Francis Pickens Miller and state senator John W. Rust) as well as at least two of his sisters.