He was Chief Librarian of the Labour Party from 1987 to 1992.
He was Political Secretary/Director of Political Operations at 10 Downing Street for Tony Blair from 2005–2007, where he provided political management and support for the development of the government's political strategy.
In December 2013 it was alleged by political blogger Paul Staines that McTernan was the inspiration for Jamie McDonald a character in the film In The Loop, who was characterised as the "crossest man in Scotland".
On 16 December 2013, on the Daily Politics show, when questioned about the rights of people to demand a referendum on leaving the European Union, McTernan said there shouldn't be a referendum and "I don't care if they [the people] want it, they want a lot of things but they can't have them".
- Totaro, Paola (2012-05-06). "Julia's master of spin". Sydney Morning Herald. Retrieved 2013-12-11.
- "John McTernan". London. The Guardian. Retrieved 21 December 2010.
- "Honours probe quiz for No 10 aide", BBC News Scotland, 24 January 2007
- "Blair aide sent to stem SNP tide", The Scotsman, 16 January 2007
- "Now Holyrood election chief quizzed in peerages inquiry", The Scotsman, 24 January 2007
- Stratton, Allegra (2011-09-28). "Allegra Stratton's conference diary: Ed and Ed learn tough lessons from Blair and Brown". The Guardian. Retrieved 2013-12-11.
- John McTernan columns for The Scotsman
- Daily Telegraph blog