John Sullivan grew up in Balham, South London, failed his eleven-plus and left school at 15 with no qualifications. From a working-class background, Sullivan's Irish father was a plumber and his mother occasionally worked as a charlady. It was in Balham where he observed the sort of market trader that would later appear in Only Fools and Horses. Sullivan's first paid employment was as a messenger boy for Reuters.

Much of Sullivan's material for Only Fools and Horses scripts came from his real-life experiences: the chandelier falling, his father's poker sessions, his niece working in the police force, and his grandfather falling down holes to claim money.

In 2005 New Years Honours, Sullivan was awarded an OBE for services to drama. On 2 September 2008 John Sullivan was awarded an Honorary Fellowship at Goldsmiths, University of London. He now lives in the city of Brighton and Hove.