He was inspired to become a diplomat after being invited to assist the former British prime minister and foreign secretary Sir Anthony Eden with his memoirs.
In the British Diplomatic Service, Cartledge served in Sweden, the Soviet Union and Iran before being appointed, in 1977, to be Private Secretary (Overseas Affairs) to the British Prime Minister; he served both James Callaghan and Margaret Thatcher in that capacity before taking up his first ambassadorial appointment as British ambassador to Hungary in 1980.
He then headed the Defence and Overseas Secretariat of the Cabinet Office, as deputy secretary of the British Cabinet, before returning to Moscow as ambassador, where he had regular dealings with Mikhail Gorbachev and Eduard Shevardnadze.
Cartledge left the Diplomatic Service in 1988 on his election to be principal of Linacre College, Oxford.
His history of Hungary, The Will to Survive, fulfils an aspiration which grew out of his deep interest in the country where he served three years as ambassador.