He entered Parliament in 1950, and wrote the book The Future Of Socialism in 1956 in which he outlined his vision for the future. He was a friend and protogé of Hugh Gaitskell and under Harold Wilson was Secretary of State for Education and Science (1964-1967, President of the Board of Trade (1967-1969).
He was seen as a leader of the right wing of the party in the 1970s, and after Labour's return to power in 1974, he was Secretary of State for the Environment, till 1976 when he was made Foreign Secretary. He died suddenly in 1977.