Sir John has had a distinguished career as a British intelligence officer, diplomat, and civil servant.
Early on, he worked in Yemen, Syria, South Africa and Washington. At home he was involved in Russian, Middle Eastern and EU policy in the Foreign and Commonwealth Office.

In 1991 Sir John became Foreign Affairs Advisor to PM Tony Blair, a period that included the Kosovo war and the Northern Ireland peace process. He became ambassador to Egypt in 2001, followed by Special Representative in Iraq, Political Director at the Foreign Office and, finally, UK's ambassador to the United Nations in 2007.

His career culminated in five years as chief of the British Secret Intelligence Service (MI6). In that role, he took part in the UK National Security Council and the Joint Intelligence Committee, contributing to assessments of the threats to UK's security in a period of high terrorist activity. He modernized the way the service works and created a more open approach to public accountability.

Upon leaving public service, Sir John became Chairman and Partner at Macro Advisory Partners until he set up Newbridge Advisory in 2019, to advise corporate leaders on geopolitics and political risk. In addition, he has pro bono roles including with King's College London, Nottingham University, the Council on Foreign Relations, and Chatham House.