Deary, the son of a butcher, was born in Sunderland, northern England. A former professional actor, theater director and drama teacher, he began writing at the age of 29. In spite of being famous for writing a series of history books, Deary does not consider himself to be a historian. He considers historians to be dishonest writers who "pick on a particular angle and select the facts to prove their case". According to his website, Deary has now stopped writing children's fiction and plans to write novels for adults in the future.