Cornwell was born in London in 1944. His father was a Canadian airman, and his mother was English, a member of the Women's Auxiliary Air Force. He was adopted and brought up in Thundersley, Essex by the Wiggins family, who were members of the Peculiar People, a strict sect who were pacifists, banned frivolity of all kinds and even medicine. After he left them, he changed his name to his mother's maiden name, Cornwell.

Cornwell was sent away to Monkton Combe School. He attended the University of London, and after graduating, worked as a teacher. He attempted to enlist in the British armed services at least three times, but was rejected on the grounds of myopia.

He then joined the BBC's Nationwide and was promoted to become head of current affairs at BBC Northern Ireland. He then joined Thames Television as editor of Thames News. He relocated to the United States in 1980 after marrying an American. Unable to get a green Card, he started writing novels, as this did not require a work permit. He later became a U.S. citizen.

As a child, Cornwell loved the novels of C. S. Forester, chronicling the adventures of fictional British naval officer Horatio Hornblower during the Napoleonic Wars, and was surprised to find that there were no such novels following Lord Wellington's campaign on land. Motivated by the need to support himself in the U.S. through writing, Cornwell decided to write such a series. He named his chief protagonist Richard Sharpe, a rifleman involved in most of the major battles of the Peninsular War.

Cornwell wanted to start the series with the Siege of Badajoz but decided instead to start with a couple of "warm-up" novels. These were Sharpe's Eagle and Sharpe's Gold, both published in 1981. Sharpe's Eagle was picked up by a publisher, and Cornwell got a three-book deal. He went on to tell the story of Badajoz in his third Sharpe novel Sharpe's Company published in 1982.

Cornwell and wife Judy co-wrote a series of novels, published under the pseudonym "Susannah Kells". These were A Crowning Mercy, published in 1983, Fallen Angels in 1984, and Coat of Arms (aka The Aristocrats) in 1986. (Cornwell's strict Protestant upbringing informed the background of A Crowning Mercy, which took place during the English Civil War.) He also published Redcoat, an American Revolutionary War novel set in Philadelphia during its 1777 occupation by the British, in 1987.

After publishing 8 books in his ongoing Sharpe series, Cornwell was approached by a production company interested in adapting them for television. The producers asked him to write a prequel to give them a starting point to the series. They also requested that the story feature a large role for Spanish characters to secure co-funding from Spain. The result was Sharpe’s Rifles, published in 1987 and a series of Sharpe television films starring Sean Bean.

A series of contemporary thrillers with sailing as a background and common themes followed: Wildtrack published in 1988, Sea Lord (aka Killer's Wake) in 1989, Crackdown in 1990, Stormchild in 1991, and a political thriller called Scoundrel in 1992.

In June 2006, Cornwell was made an Officer of the Order of the British Empire in the Queen's 80th Birthday Honours List.

Azincourt was released in the UK in October 2008. The protagonist is an archer who participates in the Battle of Agincourt, a devastating defeat suffered by the French during the Hundred Years War. His most recent book has been The Burning Land released in 2009, another of the five Saxon Stories centering around the protagonist Uhtred of Bebbanburg.

September 2010 has been scheduled for the release of his latest novel, The Fort. Set in the summer of 1779, it follows a British force of fewer than a thousand Scottish infantry backed by three sloops-of-war, which were sent to what is now Castine in the State of Maine. The War of Independence was in its third year and the Scots were the only British troops between Canada and New York. Their orders were to make a garrison that could serve as a safe haven and a naval base. The State of Massachusetts was determined to expel the British and sent a fleet of forty vessels and some one thousand infantrymen to 'captivate, kill or destroy' the invaders.

The Sharpe stories

Cornwell's best known books feature the adventures of Richard Sharpe, an English soldier during the Napoleonic Wars.

The first 11 books of the Sharpe series (beginning in chronological order with Sharpe's Rifles and ending with Sharpe's Waterloo, published in the US as Waterloo) detail Sharpe's adventures in various Peninsular War campaigns over the course of 6—7 years. Subsequently, Cornwell wrote a prequel quintology — Sharpe's Tiger, Sharpe's Triumph, Sharpe's Fortress, Sharpe's Trafalgar and Sharpe's Prey — depicting Sharpe's adventures under Wellington's command in India, including his hard-won promotion to the officer corps, his return to England and his arrival in the 95th Rifles.

He also wrote Sharpe's Battle, a novel "inserted" into his previous continuity, taking place during the Battle of Fuentes de Oñoro. It has been alleged that Cornwell was initially dubious about the casting of Sean Bean for the television adaptations, but if this is true the doubts did not last as he was subsequently so delighted that he dedicated Sharpe's Battle to him, and has admitted that he subtly changed the writing of the character to align with Bean's portrayal. Since 2003, he has written further "missing adventures" set during the "classic" Peninsular War era.

The following is the correct 'historical' order, although they are all stand alone stories:

• Sharpe's Tiger: Richard Sharpe and the Siege of Seringapatam, 1799
• Sharpe's Triumph: Richard Sharpe and the Battle of Assaye, September 1803
• Sharpe's Fortress: Richard Sharpe and the Siege of Gawilghur, December 1803
• Sharpe's Trafalgar: Richard Sharpe and the Battle of Trafalgar, October 1805
• Sharpe's Prey: Richard Sharpe and the Expedition to Copenhagen, 1807
• Sharpe's Rifles: Richard Sharpe and the French Invasion of Galicia, January 1809
• Sharpe's Havoc: Richard Sharpe and the Campaign in Northern Portugal, Spring 1809
• Sharpe's Eagle: Richard Sharpe and the Talavera Campaign, July 1809
• Sharpe's Gold: Richard Sharpe and the Destruction of Almeida, August 1810
• Sharpe's Escape: Richard Sharpe and the Bussaco Campaign, 1810
• Sharpe's Fury: Richard Sharpe & the Battle of Barrosa, March 1811
• Sharpe's Battle: Richard Sharpe and the Battle of Fuentes de Oñoro, May 1811
• Sharpe's Company: The Siege of Badajoz, January to April 1812
• Sharpe's Sword: Richard Sharpe and the Salamanca Campaign, June and July 1812
• Sharpe's Skirmish: Richard Sharpe and the defence of the Tormes, August 1812 (short story)
• Sharpe's Enemy: Richard Sharpe and the Defense of Portugal, Christmas 1812
• Sharpe's Honour: Richard Sharpe and the Vitoria Campaign, February to June 1813
• Sharpe's Regiment: Richard Sharpe and the Invasion of France, June to November 1813
• Sharpe's Christmas, 1813 (short story)
• Sharpe's Siege: Richard Sharpe and the Winter Campaign, 1814
• Sharpe's Revenge: Richard Sharpe and the Peace of 1814
• Sharpe's Waterloo: Richard Sharpe and the Waterloo Campaign, 15 to 18 June 1815
• Sharpe's Ransom, 181? (short story, appears in Sharpe's Christmas)
• Sharpe's Devil: Richard Sharpe and the Emperor, 1820—21

The Starbuck Chronicles

A tetralogy set during the American Civil War. The title character, Nathaniel Starbuck, is a Northerner who has decided to fight for the South in a Virginian regiment, the Faulconer Legion. The last novel to date in the series has been The Bloody Ground, taking place during the Antietam Campaign. Cornwell has said that he plans to write more Starbuck novels, but has not done so yet.

• Rebel
• Copperhead
• Battle Flag
• The Bloody Ground

The Warlord Chronicles

A trilogy depicting Cornwell's historical re-creation of Arthurian Britain. The series posits that Post-Roman Britain was a difficult time for the native Britons, being threatened by invasion from the Anglo-Saxons in the East and raids from the Irish in the West. At the same time, they suffered internal power struggles between their petty kingdoms and friction between the old Druidic religion and newly-arrived Christianity.

• The Winter King
• Enemy of God
• A Novel of Arthur

The Grail Quest novels

A trilogy that deals with a mid-14th century search for the Holy Grail during the Hundred Years' War. An English archer, Thomas of Hookton, becomes drawn into the quest by the actions of a mercenary soldier called "The Harlequin," who murders Thomas's family in his own obsessive search for the Grail. Cornwell was planning at one point to write more books about the main character Thomas of Hookton and said that shortly after finishing Heretic he had "... started another Thomas of Hookton book, then stopped it — mainly because I felt that his story ended in Heretic and I was just trying to get too much from him. Which doesn't mean I won't pick the idea up again sometime in the future."

• Harlequin (published in the USA under the title The Archer's Tale)
• Vagabond
• Heretic

The Saxon Stories

Cornwell's latest series focuses on the Anglo-Saxon kingdom of Wessex, England during the 9th-century reign of Alfred the Great, his fierce opposition to the Danes (Vikings), and his determination to unite England as one country. According to Cornwell's replies on his website bulletin board, the series will not be a trilogy like his medieval works, but will have 3 or 4 more sequels: "I'm not sure how many there will be — perhaps seven? maybe eight?"

The latest in the series, titled The Burning Land, was released in Britain on 1 October 2009 and in the United States in January 2010.

• The Last Kingdom
• The Pale Horseman
• The Lords of the North
• Sword Song
• The Burning Land

The Thrillers

Cornwell's thriller series are modern mysteries, all with sailing themes. He is a traditional sailor and enjoys sailing his Cornish Crabber by the name of "Royalist." His thorough knowledge of sailing and popular skills with writing combine in great novels for the nautically obsessed. According to Cornwell's website, there may be no additions to the series: "I enjoyed writing the thrillers, but suspect I am happier writing historical novels. I'm always delighted when people want more of the sailing books, but I'm not planning on writing any more, at least not now - but who knows? perhaps when I retire."

• Wildtrack (1988)
• Sea Lord (US Title: Killers Wake) (1989)
• Crackdown (1990)
• Storm Child (1991)
• Scoundrel (1992)