O'Sullivan was born on 5 December 1975 in Wordsley, West Midlands, the son of Ronald John and Maria (née Catalano) O'Sullivan, who ran a string of sex shops in the Soho area of London. He was brought up in the Manor Road area of Chigwell, Essex, where he still lives. He is a first cousin of snooker player Maria Catalano, who has been ranked number one in the women's game. In 1992, his father was sentenced to life in prison for murder and was released in 2010 after serving 18 years. His mother was sentenced to a year in prison for tax evasion in 1996, leaving O'Sullivan to care for his eight-year-old sister Danielle.