Hilary Synnott was born on 20 March 1945, son of Commander Jasper Nicholas Netterville Synnott, DSC, RN and Florence England Synnott (née Hillary). He was educated at Beaumont College, Dartmouth Naval College (scholar), Peterhouse College, Cambridge (MA) and the Royal Navy Engineering College. In 1973 he married Anne Penelope Clarke, having one son (deceased).

After serving in the Navy from 1962 to 1973 (HM Submarines, 1968-73), Synnott joined the Diplomatic Service in 1973. His career included the following posts: Foreign and Commonwealth Office, Council of Europe desk, 1973; UK Delegation to OECD, Paris [France], 1975; Bonn [West Germany, later part of Germany], 1978; Southern European Department, FCO, 1981; Head of Chancery, Amman [Jordan], 1985; Head of Western European Department, FCO, 1989; Head of Security Co-ordination Department, FCO, 1991; Minister and Deputy High Commissioner, New Delhi [India], 1993-96; Director (South and South East Asia), FCO, 1996-98; Visiting Fellow, Institute of Developing Studies, University of Sussex, and International Institute of Strategic Studies, 1999-2000; High Commissioner to Pakistan, 2000-03; Coalition Provisional Administrator, Southern Iraq, 2003-04; retired 2004. He died on 8 September 2011.