Mosley attended Eton College from 1962 to 1967, having been elected a King"s Scholar. He attended King"s College, Cambridge from 1967 to 1970, and graduated with a degree in English Literature, Philosophy and History.
He served in the Foreign & Commonwealth Office, and lived in Italy, Ireland, and France. From 2008 to 2010 Mosley was a Fellow of the Royal Society for the encouragement of Arts, Manufactures & Commerce. Mosley had a long career as an editor, becoming renowned as an international expert on genealogy and royal families.
Mosley began his career as a supply teacher in East Sussex from 1970 to 1971.
Mosley then worked on the editorial staff of the Encyclopaedia Britannica from 1971 to 1973 as a sub-editor and a librarian. From 1974 to 1977, Mosley served in the Information Research Department of the British Foreign & Commonwealth Office.
From 1977 to 1979 Mosley was based in Rome, teaching English as a second language and helping put into shape a data bank of statistics on European Community member countries. In 1980 Mosley began his association with Debrett"s Limited, becoming the first editor of Debrett"s Handbook (1981), the forerunner of Debrett"s People of Today (1983-1987).
In 1983 Mosley returned to the staff of the Encyclopaedia Britannica, serving first as Deputy London Editor then as London Editor.
In 1989 Mosley became Editor-in-Chief of Burke"s Peerage & Baronetage, a position he held until 2004, whereafter he renewed his association with Debrett"s, serving as the Editor-in-Chief of Debrett"s Limited until 2006 when he left the company to become a full-time author and broadcaster.
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Vice-chairman Families for Defence, London, 1984-1987. Member Reform Club London, Kildare Street and University Club, Dublin, Black's Club London.
Son of George Gordon and Christine Daisy Ord (Dowland) M. Married Alice Jean Hyde, March 17, 1981 (divorced August 1990). Married Lesley Vere Lake, January 18, 2003.