William Rose was born in Jefferson City, Missouri, USA, and travelled to Canada at the outbreak of World War II, while the US was still neutral, in order to join up and fight the Nazis. This took him to Britain, where he decided to stay after the war.

He spent his demobilisation money on a course in screenwriting, and then became a writer of British and American comedies such as Ladykillers, Genevieve, It's a Mad Mad Mad Mad World, and The Russians Are Coming! The Russians Are Coming!, as well as more serious films such as Guess Who's Coming to Dinner.