After winning amateur titles including the IBSF World Under-21 Snooker Championship, O'Sullivan turned professional in 1992, aged 16.

Outside his playing career, he works as a pundit for Eurosport's snooker coverage and has written crime novels, autobiographies, and a health and fitness book.

[4] At the 1991 English Amateur Championship, aged 15 years and 98 days, he made his first competitive maximum break, then the youngest player ever to do so in a recognised tournament.

Compiled in a time of 5 minutes and 8 seconds, it remains the fastest competitive maximum break in snooker history, which is listed as a Guinness World Record.

[14] After winning the 1998 Irish Masters, he was stripped of his title and prize money when a post-match drug test found evidence of cannabis in his system.

[15] O'Sullivan subsequently acknowledged frequent abuse of drugs and alcohol in the early years of his career, which resulted in spells in the Priory Hospital for rehabilitation.

During the 2005 World Championship, he shaved his head mid-tournament and exhibited what The Independent called a "public emotional disintegration" while losing 11 of the last 14 frames in his quarter-final defeat against Peter Ebdon.

[22] Trailing Hendry 4–1 in their best-of-17-frames quarter-final at the 2006 UK Championship, he abruptly conceded the match during the sixth frame and left the arena.

[17] After two poor seasons that saw him fall out of the top ten in the world rankings for the first time,[18] he began working with psychiatrist Steve Peters in 2011.

[24] A resurgent O'Sullivan captured his fourth World title in 2012, defeating Carter 18–11 in the final, after which he paid tribute to Peters' work with him.

[47] He won record-extending eighth titles at both the 2023 UK Championship and the 2024 Masters, respectively defeating Ding Junhui and Ali Carter 10–7 in the finals.

[17] Known for his fast and attacking style of play, O'Sullivan gained the nickname "The Rocket" after winning a best-of-nine frame match in a record 43 minutes during his debut season as a professional.

[57] When he first displayed this left-handed ability in the 1996 World Championship against Alain Robidoux, the Canadian accused him of disrespect and refused to shake hands after the match.

[66] In 2024, Hendry agreed that there was no longer any question as to whether O'Sullivan was the greatest snooker player of all time, also calling him an "artist".

[68] One of the most popular players on the circuit,[69] he is noted for being a "showman",[70] and is credited with helping improve the image of snooker with the general public.

[73] However, O'Sullivan sometimes lacks confidence or interest,[74] and has performed inconsistently throughout his career,[75] with observers noting the "two Ronnies" aspect of his character.

He took issue with increased travel expectations, flat 128 draws that required top professionals to play more rounds against lower-ranked opponents, reduced prize money for maximum breaks, and tournament venues he saw as inadequate.

He accused snooker's governing body WPBSA of bullying and intimidating him, claimed that Hearn was running a "dictatorship",[79] protested alleged mistreatment by snooker's authorities by giving robotic or monosyllabic responses in interviews,[80] and refused opportunities to make maximum breaks in apparent protest over inadequate prize money for the achievement.

[82] During the 2020 World Championship, O'Sullivan publicly criticised the standard of new players coming into snooker, stating that he would have to "lose an arm and a leg to fall out of the top 50".

He called snooker a "bad sport" that can cause "a lot of damage", suggesting that the antisocial nature of solitary practice in a darkened environment can stunt players' personal development.

He stated that he would not support his own children if they chose to become snooker players, and said that if he could live his sporting career over again, he would pursue golf or Formula One instead.

[85] Eurosport signed an exclusive deal with O'Sullivan in March 2014 to make him its global ambassador for snooker, with the goal of driving its international appeal.

[citation needed] In 2015 and 2016, O'Sullivan co-hosted the Midweek Matchzone show with Chris Hood on Brentwood radio station Phoenix FM.

[89] O'Sullivan has written three crime novels in collaboration with author Emlyn Rees:[90] Framed (2016),[91] Double Kiss (2017),[92] and The Break (2018).

[93] He has also co-authored a health and fitness book with nutritionist Rhiannon Lambert entitled Top of Your Game: Eating for Mind and Body.

[95] A documentary film titled Ronnie O'Sullivan: The Edge of Everything was produced by David Beckham's production company Studio 99, directed by filmmaker Sam Blair, and distributed by MetFilms.

[97] In October 2023, O'Sullivan launched an online snooker course entitled The Rocket Method, where he provides in-depth lessons on the game for a subscription fee.

[108] 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.

[127] Noted for repeatedly declaring his intention to retire,[128] O'Sullivan took an extended break from the professional snooker tour during the 2012–13 season, during which he worked on a pig farm for several weeks.

His book choice was Running with the Kenyans by Adharanand Finn, his luxury item was a painting set and his favourite disc was "That's All" by Genesis.