O’Brian is born Richard Patrick Russ, in Chalfont St. Peter, Buckinghamshire, to Charles Russ, an English physician of German descent, and Jessie Russ (née Goddard), an English woman of Irish descent. His literary career begins in his childhood with the publishing of his earliest works, including several short stories, the book Hussein, An Entertainment, and the short story collection Beasts Royal. The latter two bring him considerable critical praise especially considering his youth. He publishes his first novel, Caesar: The Life Story of a Panda Leopard, at the age of 15 with help from his father.
O’Brian is best known for his Aubrey–Maturin series of sea novels set in the Royal Navy during the Napoleonic Wars, and centered on the friendship of the English naval captain Jack Aubrey and the Irish–Catalan physician Stephen Maturin. The 20-novel series, the first of which is Master and Commander, is known for its well-researched and highly detailed portrayal of early 19th-century life, as well as its authentic and evocative language. A partially finished 21st novel in the series is published posthumously containing facing pages of handwriting and typescript.
O’Brian write a number of other novels and short stories, most of which were published before he achieves success with the Aubrey–Maturin series. He also translates works from French to English, and writes two biographies.
O’Brian’s major success as a writer comes late in life, when the Aubrey-Maturin series catches the eye of an American publisher. The series draws more readers and favourable reviews when the author is in his seventies. Near the end of his life, and in the same year he loses his beloved wife, British media reveals details of O’Brian’s early life, first marriage, and post-war change of name, causing distress to the very private author and to many of his readers at that time.
Between 1946 and 1949 O’Brian and his wife Mary live in Cwm Croesor, a remote valley in north Wales, where they initially rent a cottage from Clough Williams-Ellis. In 1949 they move to Collioure, a Catalan town in southern France. He and Mary remain together in Collioure until her death in 1998.
O’Brian dies on January 2, 2000 at Trinity College, Dublin where he had been living and working on his next book. His body is returned to Collioure, where he is buried next to his wife.