[5] He was educated at Sherborne School in Dorset, before going up to Queens' College, Cambridge,[1] where he was a major scholar and later an Honorary Fellow.

Thomas gained a first class in Part I of the History Tripos in 1952, and the following year was president of the Cambridge Union Society.

[6] From 1954 to 1957, Thomas worked in the Foreign Office partly as secretary of the British Delegation to the sub-committee of the UN Disarmament Commission.

[7] He was created a life peer as Baron Thomas of Swynnerton, of Notting Hill in Greater London by letters patent dated 16 June 1981, and sat as a Conservative, before he joined the Liberal Democrats in late 1997.

In 1985, he signed a petition against the Sandinista National Liberation Front of Nicaragua,[9] in support of the Contras, an anti-Sandinista paramilitary group.