O'Sullivan was born in Wordsley in the West Midlands. He grew up, and still lives, in the Manor Road area of Chigwell, Essex, an affluent suburb of London. He attended Wanstead High School. His parents Ronald John O'Sullivan and Maria O'Sullivan ran a string of sex shops in Soho. His father was jailed in 1992 for murder and released 18 years later.
O'Sullivan has three children: Taylor-Ann Magnus (born 1996) from a two-year relationship with Sally Magnus; Lily (born 2006) and Ronnie (born 2007) from a relationship with Jo Langley, whom he met at Narcotics Anonymous. In February 2013, he became engaged to actress and former Strictly Come Dancing contestant Laila Rouass, with whom he had been in a relationship since early 2012.
O'Sullivan is a keen football fan and is a supporter of Arsenal. He is also a keen runner, and runs for Woodford Green with Essex Ladies. He has a personal best of 34 minutes 54 seconds for 10 km races, which ranked him in the top 1500 of 10k runners in the United Kingdom in 2008. O'Sullivan also enjoys cooking, and has said that if he were to go back to school he would study cooking.
He has been labelled a perfectionist, and highly self-critical, even in victory. He suffered from clinical depression, and has had drug-related problems, but works with the sports psychologist Steve Peters, who has helped him overcome his mood swings. Noted for repeatedly declaring his intention to leave the sport, O'Sullivan worked during the 2012/2013 season on a pig farm.
I don't think I suffered with depression, I don't think I'm a depressed type of person - I just think I suffered a depression to do with snooker, and I just couldn't handle it. I could go out and play, but take me out of there and I couldn't do life. It was a nightmare, my life just felt like a bit of a nightmare.
The relentless pursuit of perfection has been my problem over the years. It's maybe held me back.