Morse was born in Madison, Wisconsin, and educated at the universities of Wisconsin, Minnesota, and Columbia, New York. He was professor of law at the University of Oregon 1931-44 and won acclaim as a labour arbitrator, serving on several federal governmental boards up to the time of his election as senator in 1945. Renowned for his support of human rights, education, progressive farm policies, and environmentalism, Morse found himself at odds with the Republican Party, declared himself an Independent in 1953, and won re-election in 1956 as a Democrat. His leadership of a senate subcommittee on Latin America influenced President John Kennedy's initiation of the Alliance for Progress in 1961, a programme for US aid to Latin American countries. He was one of two senators to vote against the Tonkin Gulf Resolution in 1964, which formed the basis for the considerable increase of US military involvement in the Vietnam War, and remained a resolute opponent of the war in Vietnam for the remainder of his career. Defeated for re-election in 1968, he was making a new bid for the senate when he died.