Born in London in 1944, his father was a Canadian airman; his mother English, a member of the Women's Auxiliary Air Force. He was given up for adoption and brought up in Essex. He attended London University and after graduating worked for BBC Television. Married Judy in 1980 and re-located to her home country, the USA. Unable to get a Green Card he started writing novels, as this did not require a work permit.
His best-known books feature the adventures of the English soldier Sharpe and are set in the Napoleonic era. After writing 12 books detailing adventures set around various European battle campaigns over the course of 12 years, further stories covered Sharpe's earlier years as a young soldier in India. Most of the Napoleonic-era books were filmed for a TV series starring Sean Bean as Sharpe. Further books written subsequently have been slotted in to different parts of Sharpe's timeframe.
Cornwell has also written the Starbuck Chronicles, four novels set during the American Civil War; and the three Warlord Chronicles dealing with Arthurian England. His latest series is the Grail Quest novels dealing with a 14th Century search for the Holy Grail.