Four-time Crucible King O'Sullivan took a break from snooker after beating Ali Carter in last year's final, but will make a much-anticipated return on the sport's biggest stage.
Hearn said: "We're delighted that Ronnie has decided to enter the World Championship, it is fantastic news for the sport. The event would not be the same without the defending champion.
"We have had a series of outstanding tournaments this season, with record ticket sales and superb viewing figures. There are many great players contesting the big titles. But Ronnie remains a fans' favourite and we welcome him back.
"The atmosphere when he steps into the Crucible arena on the first morning of the Championship will be electric. Anyone who hasn't got tickets booked for the tournament should do so immediately because it's building up to be the best ever."
As defending champion, O'Sullivan will be number one seed and will be scheduled to play on the opening day of the tournament, Saturday April 20, at 10am and 7pm.
The World Championship runs from April 20 to May 6 and will feature the top 16 seeds and 16 qualifiers.
Tickets are still on sale for selected sessions, and there are phenomenal hospitality packages available for the semi-finals and final. BOOK NOW by calling 0844 6565 147 or visiting www.sheffieldtheatres.co.uk
Ball by ball scoring and results from tournaments