Cosmo Hamilton (29 April 1870 – 14 October 1942), born Henry Charles Hamilton Gibbs, was an English playwright and novelist. He was the brother of writers A. Hamilton Gibbs and Sir Philip Gibbs.
Hamilton was born in Norwood. He took his mother's maiden name when he began to write. Hamilton was married twice: first to Beryl Faber, née Crossley Smith, who died in 1912. (She was the sister of actor C. Aubrey Smith.) Hamilton then married Julia Bolton, the former wife of playwright Guy Bolton.
His London musicals include The Catch of the Season (1904), The Belle of Mayfair (1906), The Beauty of Bath (1906). During the First World War Hamilton was a lieutenant in the Royal Naval Air Service. He later wrote a number of Broadway shows and many screenplays, and his novels were the basis for several films.
Hamilton died, aged 72, in Guildford, England. He had written dozens of novels, averaging a novel per year most of his adult life. His novels include: