Cicely Mary Hammill was born in Paddington, London, the first of four children of Denzil Hammill, captain of the 75th Regiment of the British Army, and his wife, Maude Mary Florence Hammill. In 1881 her father was sent to Egypt with the British Army, and she and her brothers and sister are boarded with another family. In 1885 her father retired from the army and returned to England, and she is reunited with him at her aunts' house in Bournemouth. She is sent to a boarding school in Malvern, Worcestershire. In 1891, she taught school while still a student herself. In 1893 she changed her name to Cicely Mary Hamilton and moved to London to act. She finds jobs mainly with touring companies. In 1903, frustrated at the lack of roles in London, she gave up acting to become a writer. To support herself and her younger sister, she writes sensational romances and thrillers for pulp magazines along with the plays she is more interested in writing. In 1908, she became politically active, joining the Women's Freedom League. Her first full-length play, Diana of the Dobson's, is run and also published. That same year she cofounded with Bessie Hatton the Women Writers' Suffrage League. During World War I she worked in the organisation of nursing care, and then joined the army as an auxiliary. Later she formed a repertory company to entertain the troops. After the war, she worked as a freelance journalist, particularly on birth control, and as a playwright for the Birmingham Repertory Company. In 1938 she was given a Civil List pension. She continued to write until her death in 1952.