John Bassett Moore led an active life of public service. Admitted to the Delaware bar in 1883, two years later he was selected as the secretary to the conference on Samoan affairs and as the U.S. secretary at the conference on North Atlantic fisheries in 1887-1888. Appointed to a faculty position at Columbia University in 1891, he often took leaves of absence for government service.

At the beginning of the Spanish-American War, he was assistant secretary of state. At the Paris peace conference he was secretary and counsel. Among his other duties was serving as a member of the Permanent Court of International Justice, which he resigned from in 1928 after seven years of service to edit a historical collection of treaties. He also wrote volumes on diplomacy, legal history, and international law.