John Kerr was born on 22 February 1942, son of Dr and Mrs J. D. O. Kerr. He was educated at Glasgow Academy, before going on to study history at Pembroke College, University of Oxford. In 1965 he married Elizabeth, daughter of Mr and Mrs W. G. Kalaugher, having two sons and three daughters.

Kerr entered the Diplomatic Service in 1966, and his career included: served Moscow [Soviet Union] (1967-68); Rawalpindi [Pakistan] (1969-70); Foreign and Commonwealth Office, Western Organisations Department (1971-74); Private Secretary to Permanent Under Secretary, FCO [Thomas Brimelow, then Michael Palliser], (1974-79); Head of Defence Division, Treasury, (1979-81); Principal Private Secretary to the Chancellor of the Exchequer [Geoffrey Howe, then Nigel Lawson], (1981-84); Head of Chancery, Washington, (1984-87); Assistant Under-Secretary of State, FCO, (1987-90); Ambassador and UK Permanent Representative to the EU, Brussels [Belgium], (1990-95); Ambassador to the United States, (1995-97); Permanent Under Secretary of State, FCO, and Head of the Diplomatic Service, (1997-2002); Secretary-General, European Convention, (2002-03).

His honours include: GCMG 2001 (KCMG 1991; CMG 1987). He was made a life peer in 2004.