He was born in London, the son of Ernest Johnston and Emma Hepburn, on 11 March 1912. He was educated at Winchester College, and Balliol College, Oxford, joining the Diplomatic Service in 1936. He was appointed Third Secretary in Tokyo 1939–1941; First Secretary in Cairo 1945–1948; and Madrid 1948–1955; Head of the China and Korea Department 1952–1954; and Counsellor in Bonn 1954–1955.