Clanchy was born in Reading in 1936, the son of Henry, a Royal Navy captain from an Irish Catholic family, and Virginia, a New Zealander, and was educated at Ampleforth College.
[2] He went up to Oxford to read history, matriculating at Merton College in 1956 and taking a second class degree three years later.
This led to the publication of Abelard: A Medieval Life in 1997, on the strength of which he was elected as a Fellow of the British Academy in 1999.
[4] Clanchy appeared on In Our Time on BBC Radio 4, firstly in 2005 regarding Peter Abelard and Héloïse d'Argenteuil,[6] and secondly discussing Magna Carta in May 2009.
In 1963 Clanchy married Joan Milne, whom he had met whilst at University; they had a daughter, Kate, and a son.