Set in the Royal Navy during the Napoleonic Wars, the series is centered on the close friendship of the captain Jack Aubrey and the physician/spy Stephen Maturin. The 20-novel series, the first of which is
Master and Commander, is known for its researched and detailed portrayal of early 19th-century life, as well as its authentic and evocative language. A partially finished 21st novel in the series was published posthumously containing facing pages of handwriting and typescript. The 10th novel in the series was turned into a feature film starring Russell Crowe.
O'Brian wrote a number of other novels and short stories, most of which were published before he achieved success later in life with the Aubrey–Maturin series. He also translated works from French to English, and wrote two biographies.