The world champion planned to take a six-month sabbatical following his May triumph at the Crucible, to consider his future - and has decided to continue playing.
"[After] the six-month sabbatical I said I would [take] I am now looking forward to competing over the rest of this season," he said.
"I am happy to be back in snooker and seeing all my fans soon."
O’Sullivan has signed the WSL Players Contract and entered both the International Championship to be held in Chengdu, China and the UK Championship in York scheduled for December.
World Snooker chairman Barry Hearn said: “I met with Ronnie last night and following our discussion he has signed the WSL Players Contract.
"We are obviously very pleased that Ronnie has decided to come back to snooker, the sport he loves. This is great news for his many fans around the world.
"We welcome him back with open arms.”
O'Sullivan has missed two ranking events so far this season and dropped to 15th in the world rankings.
Only the top 16 players qualify directly for the main draw of the season-ending World Championship.