He served as a member of the NAACP's national legal committee, director and member of its executive committee, and president of board of the NAACP Legal Defense and Educational Fund. Coleman was also a member of President Dwight D. Eisenhower's Committee on Government Employment Policy (1959–1961) and a consultant to the U.S. Arms Control and Disarmament Agency (1963–1975). Coleman served as an assistant counsel to the President's Commission on the Assassination of President Kennedy (1964), also known as the Warren Commission, on which then-Congressman Gerald Ford was a commissioner.