Sir Paul served in the Diplomatic Service from 1966 to 2003, specialising in defence, security, and EU affairs. His overseas postings included Helsinki, the UK Delegation to NATO, and the European Commission. He negotiated the Treaty on Conventional Forces in Europe in Vienna in 1990 and was later Chairman of the Joint Intelligence Committee in the Cabinet Office and Director General for EU and Economic Affairs in the Foreign Office. He was Ambassador to Germany from 1997 to 2003.
After his retirement from the public service, he was Global Development Director at RWE Thames Water, a non-executive Director of Sellafield Ltd and, from 2004 to 2009, Chairman of the Royal United Services Institute. His book, Berlin Rules: Europe and the German Way, was published in 2017.