Stewart Eldon was born 18 September 1953, son of John Hodgson Eldon and of Rose Helen (née Stinton). He was educated at Pocklington School, and Christ’s College, University of Cambridge (BA Electrical Sciences 1974; MSc 1976; MA 1977). In 1978 he married Christine Mary Mason, having one son and one daughter.

Eldon joined the Diplomatic Service in 1976, and during his career served in the following posts: UK Mission to United Nations, New York [United States], 1976; Foreign and Commonwealth Office, 1977; Third, later Second Secretary, Bonn [Germany], 1978-82; First Secretary, FCO, 1982; Private Secretary to Minister of State, 1983-86; First Secretary, UK Mission to United Nations, New York, 1986-90; Assistant Head, Middle East Department, FCO (also Deputy Crisis Manager, Gulf War), 1990-91; Counsellor, European Secretariat, Cabinet Office, 1991-93; Fellow, Center for International Affairs, Harvard University, 1993-94; Counsellor (Political), UK Delegation to NATO, Brussels [Belgium], 1994-97; Director (Conferences), FCO, 1997-98; Ambassador and Deputy Permanent Representative, UK Mission to United Nations, New York, 1998-2002; Ambassador to Ireland, 2003-06; UK Permanent Representative, UK Delegation to NATO, 2006-10; NATO Subject Matter Expert on Building Integrity, 2010 onwards.