John Weston was born on 13 April 1938, son of Philip George Weston and Edith Alice Bray (née Ansell); he was educated at Sherborne, then Worcester College, Oxford, taking a 1st Class in Classics. In 1967 he married Margaret Sally Ehlers; they had two sons and one daughter.

After his National Service with the Royal Marines, (1956-58), Weston entered the Diplomatic Service in 1962. His career included: Foreign Office, (1962-63); Treasury Centre for Administrative Studies, (1964); Chinese Language student, Hong Kong, (1964-66); Peking [China], (1967-68); FO, (1969-71); Office of British Permanent Representative to European Economic Community, (1972-74); Assistant Private Secretary to Foreign Secretary [(Leonard) James Callaghan, then (Charles) Anthony Crosland), (1974-76); Counsellor, Head of EEC Presidency Secretariat, Foreign and Commonwealth Office, (1976-77); Visiting Fellow, All Souls College, Oxford, (1977-78); Counsellor, Washington [United States], (1978-81); Head of Defence Department, FCO, (1981-84); Assistant Under-Secretary of State, FCO, (1984-85); Minister, Paris [France], (1985-88); Deputy Secretary to Cabinet, Cabinet Office, (1988-89) (on secondment); Deputy Under-Secretary of State (Defence), FCO, (1989-90); Political Director, FCO, (1990-91); Ambassador and British Permanent Representative to North Atlantic Council (NATO), (1991-95), to Permanent Council of Western European Union, (1992-95); British Permanent Representative to the United Nations, (1995-98).