John Thomson was born 27 April 1927, son of Sir George Thomson, FRS, Master of Corpus Christi College, University of Cambridge, and Kathleen. He was educated at Phillips Exeter Academy, USA, the University of Aberdeen and Trinity College, University of Cambridge. Thomson married (1st) in 1953, Elizabeth Anne McClure (d 1988), daughter of Norman McClure, President of Ursinus College, Pennsylvania, having three sons and one daughter, and (2nd) in 1992, Judith Ogden Bullitt, daughter of John Stanley Ogden, New York, and Olga Geddes Bradshaw, Melbourne.

Thomson entered the Foreign Office in 1950 and his diplomatic career included the following posts: Third Secretary, Jedda [Saudi Arabia], 1951; Damascus [Syria], 1954; FO, 1955; Private Secretary to Permanent Under-Secretary, 1958-60; First Secretary, Washington [United States], 1960-64; FO, 1964; Acting Head of Planning Staff, 1966; Counsellor, 1967; Head of Planning Staff, FO, 1967; seconded to Cabinet Office as Chief of Assessments Staff, 1968-71; Minister and Deputy Permanent Representative to North Atlantic Council, 1972-73; Head of UK Delegation to MBFR (the Mutual and Balanced Force Reductions) Exploratory Talks, Vienna, 1973; Assistant Under-Secretary of State, Foreign and Commonwealth Office, 1973-76; High Commissioner to India, 1977-82; UK Permanent Representative to United Nations, 1982-87. Sir John died on 3 June 2018.