[1] After completing his degree at Oxford, he was a law clerk for Associate Justice of the Supreme Court of the United States Harold Hitz Burton in 1951 and 1952.
[2] He was later named as head of the United States Department of Justice Civil Division, where he was assigned by United States Attorney General Robert F. Kennedy to coordinate logistical and security considerations of the August 1963 March on Washington for Jobs and Freedom together with Bayard Rustin and other organizers of the event, an event that culminated with Martin Luther King Jr.'s "I Have a Dream" speech.
Victor S. Navasky, biographer of Robert F. Kennedy's Justice Department, stated that Douglas "shares historic credit for the orderliness and smoothness and joy of that day".
[2] In 1966, he left the Department of Justice to work on his father's bid for a fourth term in the Senate, a race he lost to Republican Charles H. Percy.
While with the law firm of Covington & Burling, he continued his advocacy work at the Washington Lawyers' Committee for Civil Rights and Urban Affairs, as president of the National Legal Aid and Defender Association and as chairman of the Carnegie Endowment for International Peace.