Career
He is nicknamed The Storm. O'Sullivan turned professional in 2012 after qualifying via Event 2 of the Q School and gained a two year tour card for the 2012/13 and 2013/14 snooker seasons. In the event, he beat Christopher Keogan 4–1, Nick Dyson 4–0, Mohammed Al Shaikh from Bahrain 4–1 and Michael Wild 4–3, before seeing off Ryan Causton 4–1 in the quarter-finals.
Debut season
O'Sullivan lost his first nine matches as a professional, picking up his first victory in the minor-ranking European Tour Event 3 by beating David Gilbert 4–3, before losing 4–2 to Jimmy Robertson. His best run of results came in qualifying for the China Open, where he defeated Craig Steadman and Alfie Burden, but then lost 5–3 to Rory McLeod. O'Sullivan's season ended when he was beaten 10–6 by Michael Wasley in the first round of World Championship Qualifying.
He finished his first year on tour ranked world number 91. 2013/2014 season
He dropped off the tour at the end of the season as he was ranked world number 102, well outside of the top 64 who retain their places. 2014/2015 season
At the Riga Open in August 2014, O'Sullivan reached his first quarter-final in a professional event with wins over Jamie Burnett, Mark Joyce, Jak Jones and Mark Davis, before he was beaten 4–0 by Mark Allen.