Brian Donnelly was born 24 April 1945, son of Joseph Donnelly and Ada Agnes (née Bowness). He was educated at Workington Grammar School, Queen’s College, University of Oxford (Wyndham Scholar, MA; Hon. Fellow, 2015) and the University of Wisconsin (MA). In 1966 he married (1st), Susanne Gibb (marriage dissolved 1994), having one daughter, and (2nd) in 1997, he married Julia Mary Newsome, having one step son and one step daughter.

Donnelly began as an Administrative trainee at GCHQ in 1970, but joined the Diplomatic Service in 1973. His diplomatic career included the following: 2nd Secretary, Foreign and Commonwealth Office, 1973; 1st Secretary, UK Mission to United Nations, New York [United States], 1975-79; Head of Chancery, Singapore, 1979-82; Assistant Head, Personnel Policy Department, FCO, 1982-84; Deputy to Chief Scientific Adviser, Cabinet Office, 1984-87; Counsellor and Consul General, Athens [Greece], 1988-91; Royal College of Defence Studies, 1991; Head of Non-Proliferation Department, FCO, 1992-95; Minister and Deputy Permanent Representative, UK Delegation to NATO and Western European Union, Brussels [Belgium], 1995-97; Ambassador to Yugoslavia [later Bosnia and Herzegovina, Croatia, Kosovo, Montenegro, North Macedonia, Serbia, and Slovenia], 1997-99; Director and Special Representative for SE Europe, FCO, 1999-2000, on secondment to BP Amoco, 2000-01; Ambassador (formerly High Commissioner) to Zimbabwe, 2001-04; Special Adviser to Foreign Secretary, 2005-06; Visiting Directing Staff, RCDS, 2007-09.