Magdalen King-Hall was born in London and as a girl lived in Australia, where her father, Admiral Sir George Fowler King-Hall, served as the Royal Navy's Commander-in-Chief. She was educated at Downe House and St. Leonard's near St. Andrews, and became a journalist and writer. In 1929, she married a distant cousin, Patrick Perceval Maxwell, with whom she had three children. They lived for a while in the Sudan, where Maxwell worked for the Sudan Cotton Plantation Syndicate. In 1932 they returned to England and a few years later moved to Northern Ireland, where Maxwell farmed near his family home. She wrote numerous successful historical novels, nonfiction, and children's books. Her debut novel, Diary of a Young Lady of Fashion, 1764-65 (1924), written under the pseudonym Cleone Knox, describing the experiences of young woman on a Grand Tour of Europe, was enthusiastically received by reviewers, some of whom believed it was an actual 18th-century document, and became a bestseller. Her 1954 novel, Life And Death of the Wicked Lady Skelton (aka The Wicked Lady), was twice adapted into films. Her sister Lou (Olga Louisa Elizabeth) Hall-King also became a novelist. Her brother Stephen Hall-King was a British naval officer and writer.