Cornwell was born on 19 October 1931 in Poole, Dorset, England. His father was Ronald Thomas Archibald (Ronnie) Cornwell (1906–75), and his mother was Olive Moore Cornwell (née Glassey, b. 1906). His older brother, Tony (1929–2017), was an advertising executive and former county cricketer (for Dorset), who lived in America. His younger half-sister is the actress Charlotte Cornwell. His younger half-brother, Rupert Cornwell, is a former Washington bureau chief for the newspaper The Independent. Cornwell said he did not know his mother, who abandoned him when he was five years old, until their re-acquaintance when he was 21 years old. His father had been jailed for insurance fraud, was an associate of the Kray twins, and was continually in debt. Their father/son relationship was difficult. A biographer reports, “His father, Ronnie, made and lost his fortune a number of times due to elaborate confidence tricks and schemes which landed him in prison on at least one occasion. This was one of the factors that led to le Carré’s fascination with secrets.”

From 1948 to 1949, he studied foreign languages at the University of Bern in Switzerland. In 1950, he joined the Intelligence Corps of the British Army garrisoned in Allied-occupied Austria, working as a German language interrogator of people who crossed the Iron Curtain to the West. In 1952, he returned to England to study at Lincoln College, Oxford, where he worked covertly for the British Security Service, MI5, spying on far-left groups for information about possible Soviet agents. During his studies, he was a member of a dining society known as The Goblin Club.

When his father was declared bankrupt in 1954, Cornwell left Oxford to teach at Millfield Preparatory School; however, a year later he returned to Oxford, and graduated in 1956 with a first class degree in modern languages. He then taught French and German at Eton College for two years, becoming an MI5 officer in 1958. He ran agents, conducted interrogations, tapped telephone lines and effected break-ins. Encouraged by Lord Clanmorris (who wrote crime novels as “John Bingham”), and whilst being an active MI5 officer, Cornwell began writing his first novel, Call for the Dead (1961). Cornwell has identified Lord Clanmorris as one of two models for George Smiley, the spymaster of the Circus, the other being Vivian H. H. Green. As a schoolboy, Cornwell first met the latter when Green was the Chaplain and Assistant Master at Sherborne School (1942–51). The friendship continued after Green’s move to Lincoln College, where he tutored Cornwell.

In 1954, Cornwell married Alison Ann Veronica Sharp; they had three sons—Simon, Stephen and Timothy—and divorced in 1971. In 1972, Cornwell married Valérie Jane Eustace, a book editor with Hodder & Stoughton; they have one son, Nicholas, who writes as Nick Harkaway. Le Carré has lived in St Buryan, Cornwall for more than 40 years; he owns a mile of cliff near Land’s End.

In 1960, Cornwell transferred to MI6, the foreign-intelligence service, and worked under the cover of Second Secretary at the British Embassy at Bonn; he was later transferred to Hamburg as a political consul. There, he wrote the detective story A Murder of Quality (1962) and The Spy Who Came in from the Cold (1963), as “John le Carré” (le Carré is French for “the square”)—a pseudonym required because Foreign Office officers were forbidden to publish in their own names.

In 1964, le Carré’s career as an intelligence officer came to an end as the result of the betrayal of British agents’ covers to the KGB by Kim Philby, the infamous British double agent (one of the Cambridge Five). He left the service to work as a full-time novelist. Le Carré depicts and analyses Philby as the upper-class traitor, codenamed “Gerald” by the KGB, the mole hunted by George Smiley in Tinker Tailor Soldier Spy (1974).

In 1964, le Carré won the Somerset Maugham Award (established to enable British writers younger than 35 to enrich their writing by spending time abroad).

Rick Pym, Magnus Pym’s father, a scheming con-man in A Perfect Spy, was based on Ronnie. When his father died in 1975, Cornwell paid for a memorial funeral service but did not attend it.

With the fall of the Iron Curtain in 1989, le Carré’s writing shifted to portrayal of the new multilateral world. His first completely post-Cold War novel, The Night Manager (1993), deals with drug and arms smuggling in the murky world of Latin American drug lords, shady Caribbean banking entities, and western officials who look the other way.

In 1998, he was awarded an Honorary Degree (Doctor of Letters) from the University of Bath. In 2008 he was awarded an honorary doctorate from the University of Bern. In 2012, he was awarded the Degree of Doctor of Letters, honoris causa, by the University of Oxford.

In February 1999, le Carré was the guest in an episode of BBC Radio 4’s Bookclub broadcast with presenter James Naughtie and an audience in Penzance.

In January 2003, two months prior to the invasion, The Times published le Carré’s essay “The United States Has Gone Mad” criticising the buildup to the Iraq War and President George W. Bush’s response to the September 11, 2001, terrorist attacks, calling it “worse than McCarthyism, worse than the Bay of Pigs and in the long term potentially more disastrous than the Vietnam War” and “beyond anything Osama bin Laden could have hoped for in his nastiest dreams”. Le Carré contributed it to a volume of political essays titled Not One More Death (2006). Other contributors include Richard Dawkins, Brian Eno, Michel Faber, Harold Pinter, and Haifa Zangana.

In 2008, The Times ranked him 22nd on its list of “The 50 greatest British writers since 1945”.

In October 2008, a television interview on BBC Four was broadcast, in which Mark Lawson asked him to name a “Best of le Carré” list of books; the novelist answered: The Spy Who Came in from the Cold, Tinker Tailor Soldier Spy, The Tailor of Panama and The Constant Gardener.

In 2009, he donated the short story “The King Who Never Spoke” to the Oxfam “Ox-Tales” project, which included it in the project’s Fire volume.

After many years of working with various producers who made film adaptations of his novels, two of Cornwell’s sons, Simon and Stephen, founded the production company Ink Factory in 2010. This was to produce adaptations of his works as well as other film productions. The Ink Factory has produced the films A Most Wanted Man and Our Kind of Traitor, and the TV series The Night Manager and The Little Drummer Girl.

In 2010, le Carré donated his literary archive to the Bodleian Library, Oxford. The initial 85 boxes of material deposited included handwritten drafts of Tinker Tailor Soldier Spy and The Constant Gardener. The library hosted a public display of these and other items to mark World Book Day in March 2011.

In September 2010, le Carré was interviewed at his house in Cornwall by the journalist Jon Snow for Channel 4 News. The conversation involved several topics: his writing career generally and processes adopted for writing (specifically about his latest book, Our Kind of Traitor, involving Russia and its current global influences, financial and political); his SIS career, discussing why – both personally and more generally – one did such a job then, as compared to now; and how the earlier fight against communism had now moved to the hugely negative effects of certain aspects of excessive capitalism. During the interview he said that it would be his last UK television interview. While reticent about his exact reasons, those he was willing to cite were that of slight self-loathing (which he considered most people feel), a distaste for showing off (he felt that writing necessarily involved a lot of this anyway) and an unwillingness to breach what he felt was the necessarily solitary nature of the writer’s work. He was also wary of wasting writing time and dissipating his talent in social success, having seen this happen to many talented writers, to what he felt was the detriment of their later work.

The December 2010 Channel 4 broadcast John Le Carre: A Life Unmasked was described as his “most candid” television interview.

Credited by his pen name, le Carré appeared as an extra in the 2011 film version of Tinker Tailor Soldier Spy, among the guests at the Christmas party in several flashback scenes. He records a number of incidents in his autobiographical The Pigeon Tunnel. Stories from My Life (2016) from his period as a diplomat; including escorting six visiting German parliamentarians to a London brothel and translating at a meeting between a senior German politician and Harold Macmillan.

In 2011, he won the Goethe Medal, a yearly prize given by the Goethe Institute.

Le Carré was interviewed at the Hay on Wye festival on 26 May 2013. The video of the event is offered for sale by le Carré to raise money to keep Hay Library open.

In 2017, le Carré stated, “I think of all things that were happening across Europe in the 1930s, in Spain, in Japan, obviously in Germany. To me, these are absolutely comparable signs of the rise of fascism and it’s contagious, it’s infectious. Fascism is up and running in Poland and Hungary. There’s an encouragement about”.

Le Carré appeared on 60 Minutes with Steve Kroft in September 2017.

When interviewed by Marian Finucane on RTÉ Radio 1 on 26 October 2019, le Carré stated that he has taken an Irish passport; qualifying through his grandmother Olive Wolfe who was born in Rosscarbery.

He won the Olof Palme Prize in 2020 and donated the $100,000 winnings to Médecins Sans Frontières.