Born in Lancashire, Hart was educated at Cheltenham College and Leicester University, then went to Oxford Polytechnic (now Oxford Brookes University) where he studied English and Art History, and Birkbeck College, London, where he obtained a PhD on W.B.Yeats.
Under his original name he has written two contemporary novels, The Harvest and Rescue Me. Since 2001, he has written four historical novels under the pseudonym of William Napier, the last three a best-selling trilogy about Attila the Hun and the Fall of the Roman Empire.
As a journalist he has worked as Literary Editor of the Erotic Review (magazine folded) and Agony Aunt for Time Out (sacked.) He currently writes regularly for the Sunday Times, where he is lead theatre critic, and the Daily Mail. He is a first cousin of Vanessa Feltz.