John Diamond, Baron Diamond PC (Leeds, April 30 1907-Chalfont St Giles, April 3 2004) was a British Labour politician.

Diamond was educated at Leeds Grammar School and became an accountant.

Diamond was elected Member of Parliament in 1945 for the Blackley division of Manchester, but lost it in 1951. In 1946 and 1947, he was parliamentary private secretary to the Ministry of Works. He returned to the House of Commons in a 1957 by-election for Gloucester, caused by the death of its Labour MP, Moss Turner-Samuels . He served as Chief Secretary to the Treasury from 1964, a cabinet position from 1968, and Privy Councillor from 1965. He represented Gloucester until his surprise defeat in 1970 by Conservative, Sally Oppenheim .

Diamond was made a life peer as Baron Diamond of the City of Gloucester on 25 September 1970. In 1981 he left the Labour Party for the new Social Democratic Party. He led the SDP in the House of Lords from 1982 to 1988 but opposed its merger with the Liberals and rejoined Labour in 1995.

Diamond was first married in 1932 and had two sons and a daughter. He had a daughter by his second wife, whom he married in 1948. They separated in 1966 and divorced 10 years later. He was survived by his children and his third wife, Barbara Kagan, whom he married in 1976.

See also John Diamond, the UK journalist