White was born in Bombay, British India to English parents, Garrick Hansbury White, an Indian police superintendent, and Constance White. Terence White had a discordant childhood, with an alcoholic father and an emotionally frigid mother, and his parents separated when Terence was fourteen. White went to Cheltenham College in Gloucestershire, a public school, and Queens' College, Cambridge, where he was tutored by the scholar and occasional author L. J. Potts. Potts became a lifelong friend and correspondent, and White later referred to him as "the great literary influence in my life." While at Queens' College, White wrote a thesis on Thomas Malory's Le Morte d'Arthur (without reading it), and graduated in 1928 with a first-class degree in English.

White then taught at Stowe School, Buckinghamshire, for four years. In 1936 he published England Have My Bones, a well-received memoir about a year spent in England. The same year, he left Stowe and lived in a workman's cottage, where he wrote and "revert[ed] to a feral state", engaging in falconry, hunting, and fishing. White also became interested in aviation, partly to conquer his fear of heights. White wrote to a friend that in autumn 1937, "I got desperate among my books and picked [Malory] up in lack of anything else. Then I was thrilled and astonished to find that (a) The thing was a perfect tragedy, with a beginning, a middle and an end implicit in the beginning and (b) the characters were real people with recognisable reactions which could be forecast[...] Anyway, I somehow started writing a book." The novel, which White described as "a preface to Malory", was titled The Sword in the Stone and told the story of the boyhood of King Arthur. White was also influenced by Freudian psychology and his lifelong involvement in natural history. The Sword in the Stone was well-reviewed and was a Book of the Month Club selection in 1939.

In February 1939, White moved to Doolistown, Ireland, where he lived out the international crisis and the Second World War itself as a de facto conscientious objector. It was in Ireland that he wrote most of what would later become The Once and Future King; two sequels to The Sword and the Stone were published during this time: The Witch in the Wood (later retitled The Queen of Air and Darkness) in 1939, and The Ill-Made Knight in 1940. The version of The Sword in the Stone included in The Once and Future King differs in several respects from the earlier version. It is darker, and some critics prefer the earlier version . White's indirect experience of the war had a profound effect on these tales of King Arthur, which include commentaries on war and human nature in the form of a heroic narrative.

In 1946, White settled in Alderney, third largest of the Channel Islands, where he lived for the rest of his life. The same year, White published Mistress Masham's Repose, a children's book in which a young girl discovers a group of Lilliputians (the tiny people in Swift's Gulliver's Travels) living near her house. He hosted Julie Andrews, her then-husband Tony, and became close friends with them at this time. In 1947, he published The Elephant and the Kangaroo, in which a repetition of Noah's Flood occurs in Ireland. In the early 1950s White published two non-fiction books: The Age of Scandal (1950), a collection of essays about 18th-century England, and The Goshawk (1951), an account of White's attempt to train a hawk in the traditional art of falconry. In 1954 White translated and edited The Book of Beasts, an English translation of a medieval bestiary originally written in Latin.

In 1958 White completed the fourth book of The Once and Future King sequence, The Candle in the Wind, though it was first published with the other three parts and has never been published separately. The Broadway musical Camelot was based on The Once and Future King, as was the animated film The Sword in the Stone.

He died on 17 January 1964 aboard ship in Piraeus (Athens, Greece) of a heart ailment, en route to Alderney from a lecture tour in the United States.

He is buried in First Cemetery of Athens. In 1977 The Book of Merlyn, a conclusion to The Once and Future King, was published posthumously.

Personal life

According to Sylvia Townsend Warner's biography, White was "a homosexual and a sado-masochist." He came close to marrying several times but had no enduring romantic relationships, and wrote in his diaries that "It has been my hideous fate to be born with an infinite capacity for love and joy with no hope of using them." Broadcaster Robert Robinson has published an account of a bizarre conversation with White, in which he claimed to be attracted to small girls. Robinson concluded that this was really a cover for homosexuality. White's long time friend and literary agent, David Higham, wrote "Tim was no homosexual, though I think at one time he had feared he was [and in his ethos fear would have been the word]." Higham gave Warner the address of one of White's lovers "so that she could get in touch with someone so important in Tim's story. But she never, the girl told me, took that step. So she was able to present Tim in such a light that a reviewer could call him a raging homosexual. Perhaps a heterosexual affair would have made her blush". White was also an agnostic, and towards the end of his life a heavy drinker. Warner wrote of him, "Notably free from fearing God, he was basically afraid of the human race."

Science-fiction writer Michael Moorcock enjoyed White's The Once and Future King, and was especially influenced by the underpinnings of realism in his work. Moorcock eventually engaged in a "wonderful correspondence" with White, and later recalled that "White [gave] me some very good advice on how to write".

J. K. Rowling has said that T. H. White's writing strongly influenced the Harry Potter books; several critics have compared Rowling's character Albus Dumbledore to White's absent-minded Merlyn, and Rowling herself has described White's Wart as "Harry's spiritual ancestor." When asked about the similarities between Harry Potter and his earlier character Timothy Hunter, Neil Gaiman stated he did not think Rowling had based her character on Hunter, stating "I said to [the reporter] that I thought we were both just stealing from T.H. White: very straightforward."

Gregory Maguire was influenced by "White's ability to be intellectually broadminded, to be comic, to be poetic, and to be fantastic" in the writing of his 1995 novel Wicked, and crime fiction writer Ed McBain also cited White as an influence.