Born Mary Challans (Renault was a pen name), she was the daughter of a London physician. At age 8, she decided to be a writer. At Oxford, she studied medieval history and used her knowledge of the era as background for her first novel, which she destroyed after many rejections. Renault worked as a nurse during World War I and continued to write in her off-duty hours. In 1939, her novel Promise of Love, based on her nursing experiences, was published in the United States. In 1946, her novel Return to Night won the $150,000 Metro-Goldwyn-Mayer Prize. Although the book became her first U.S. bestseller, it was never made into a movie.
After World War II, Renault turned her attention to historical fiction. Fascinated by ancient Greece, she traveled widely in the area and became a self-taught expert on the region’s history. Her 1958 novel, The King Must Die, and its sequel, The Bull from the Sea (1962), retold the Greek myth of Theseus from an historically accurate point of view. All her historical novels, including The Alexander Trilogy (1984), about Alexander the Great, were widely praised both for their rich, accurate detail and lively storytelling. Renault settled in South Africa, where she lived until her death in 1983.