Peter Longworth was born on 26 May 1942, son of Frank and Edith Longworth. He was educated at Chislehurst and Sidcup Grammar School and the University of Sheffield, and in 1975 married Christina Margareta Wallin.

Longworth began his career as a journalist, 1963-74, working as Labour and Industrial Correspondent, Bristol Evening Post, 1964-66, Lobby Correspondent, Western Daily Press, 1966-68 and Diplomatic Correspondent, Westminster Press, 1968-74. He then joined the Foreign and Commonwealth Office in 1974 and his diplomatic career included the following posts: First Secretary, FCO, 1974-77; First Secretary (Economic), Bonn [Germany], 1977-81; Head of Chancery and HM Consul, Sofia [Bulgaria], 1981-84; FCO (Assistant Head of Energy, Science and Space Department), 1984-87; Counsellor (Economic and Commercial), Copenhagen [Denmark], 1987-91; Deputy Head of Mission, Counsellor (Economic and Commercial) and Consul General, Seoul [South Korea], 1991-94; Consul General, Johannesburg, and Director of UK Trade Promotion and Investment, South Africa, 1994-98; High Commissioner, Zimbabwe, 1998-2001.