Helen de Guerry Simpson was born in Sydney, Australia, the daughter of Edward Percy Simpson, a prominent lawyer, and his wife Anne de Guerry de Lauret, daughter of a French aristocrat. After her parents separated, Helen was sent to a Catholic convent boarding school and Abbotsleigh School for Girls. In 1914, she went to England to join her mother and continue her education. She entered Oxford University but interrupted her studies near the end of World War I, when she joined the Women's Royal Naval Service and interpreted and deciphered coded messages. She then went back to Oxford and studied music but left without taking her degree. She became interested in the theater and began writing short plays. She made her publishing debut with a small volume of poetry in her own translations from French, Italian, and Spanish, called Philosophies in Little (1921). In 1922, her play, A Man of his Time, based on the life of Benvenuto Cellini, won an Australian newspaper literary competition and was staged by a repertory company in Sydney, making her famous in Australia. Her first novel, Acquittal, a detective story, appeared in 1925, followed by a book of short stories, The Baseless Fabric (1925), the play The Women's Comedy (1926), and Cups, Wands and Swords (1927). In England in 1927, she married Denis John Browne, a pediatric surgeon, with whom she had a daughter. Helen was a keen horsewoman and fencer, collected antiques, cookbooks, and works on witchcraft, played piano and flute, and lectured and broadcasted on literary and historical subjects. Her 1932 novel Boomerang won the James Tait Black Memorial Prize for fiction and was serialized for radio in 1937. She wrote two historical biographies, The Spanish Marriage (1933) and Henry VIII (1934), and an historical novel, Saraband for Dead Lovers (1935). With her close friend Clemence Dane, she wrote three detective novels, the first of which, Enter Sir John (1929), was filmed as Murder! by Alfred Hitchcock, who also directed the film version of her 1937 novel Under Capricorn in 1948. In 1939, Helen de Guerry Simpson was selected by the Liberal Party as its candidate for a seat in Parliament for the Isle of Wight in upcoming elections. She traveled around England for speaking engagements before becoming ill. She was diagnosed with cancer and died after surgery at age 42. Her final novel, Maid No More, was published in 1940.