Terry was born in Sunderland, England, in 1946 and now lives in County Durham, in the North-east of England.

Terry's father (Billy) was a butcher in Hendon, Sunderland, and his mother (Freda) was the manageress of a clothing shop. He worked many years in his father's butcher shop as a boy. It was better than school where he was beaten, bullied and abused by his loathsome teachers.

Terry began his career as a professional actor in 1972 when he joined Theatre Powys in Mid-Wales. As an actor with Theatre Powys Terry began writing scripts for some of the shows. One of the most successful was a children's show called ""The Custard Kid"". The ""Custard Kid"" tour ended but Terry didn't want to lose the exciting tale so he turned it into a children's novel, published by A & C Black.

He has also worked as a theatre-director, museum manager, drama teacher, television presenter. He has written and acted for television since 1974 and scripted and appearing in British movies.

In 48 years as an author his writing has included fiction and popular non-fiction for children and adults. He has published 354 books in 45 languages and sold over 38 million copies.

In 2009 CBBC Television launched a major television series of his Horrible Histories which has gone on to win several Children's BAFTA awards. In February 2011 the TV series won a British Comedy Award for best sketch show - the first children's show ever to win a Comedy Award. The same month Terry Deary became the 10th most-borrowed author in British libraries.

A series of theatre plays, 'Horrible Histories', have been created in collaboration with Birmingham Stage Company touring the UK, Australia, the Middle East and Far East.

Terry's adult non-fiction title 'A history of Britain in Ten Enemies' (Penguin-Transworld) appeared in 2024 and his first adult murder-mystery 'Actually I'm a murderer' (Constable & Robinson) in 2025.