Mark Pellew was born on 28 August 1942, eldest son of Commander Anthony Pownoll Pellew, RN and of Margaret Julia Critchley (née Cookson). He was educated at Winchester and Trinity College, University of Oxford, and in 1965 married Jill Hosford Thistlethwaite, having two sons.

Pellew entered the Diplomatic Service in 1965 and his career included: Foreign Office, 1965-67; Third Secretary, Singapore, 1967-69; Second Secretary, Saigon [Vietnam], 1969-70; Foreign and Commonwealth Office, 1970-76; First Secretary, Rome [Italy], 1976-80; Assistant Head of Personnel Operations Department, FCO, 1981-83; Counsellor: Washington [United States], 1983-89; on secondment to Hambros Bank, 1989-91; Head of North America Department, FCO, 1991-96; Ambassador to the Holy See, 1998-2002.