O'Sullivan begins his bid when the tournament gets underway on S aturday and his first hurdle after participating in just one event since lifting the 2012 trophy will be Scotland's world number 27 Campbell.
O'Sullivan overcame Ali Carter to win his fourth championship last year, but has been out of the sport for the best part of a year. He has spent some time working on a farm, but conceded he had missed the game.
New sponsors Betfair responded to the draw for the tournament by installing O'Sullivan as joint 6-1 favourite for the tournament alongside world number one Mark Selby and 2010 winner Neil Robertson.
Speaking at a press conference in London, O'Sullivan said: "In some ways to win this year would be a fairy tale dream, but I consider last year's win my greatest achievement.
"The reason I chose to come back was I felt I needed some focus in my life, I've done the farm thing and that done my head in!
"I came back to snooker, to get back all the things I realised I missed from my life. It could be a car crash but if I'm cueing ok, then I should be a match for anyone.
"I've been running a lot, I've lost a stone since I announced my return. I have to try and keep up with the younger players!
"I've been practising 4/5 hours a day, which is hard as I lose concentration after two."
Selby drew Matthew Selt, and the Leicester player was quick to admit O'Sullivan is the man to beat. "This would be one of my best chances, if Ronnie wasn't showing up," he said.
"I couldn't take time out, I'm the sort of player who has to keep working at his game."
Third-ranked Judd Trump will begin against Dominic Dale. Four-times Crucible winner John Higgins meets Mark Davis while another ex-world champion in Mark Williams has an all-Welsh opener against Michael White.
There will be a repeat of the 2006 final when Graeme Dott meets Peter Ebdon, while Jack Lisowski makes a tough Crucible debut against Australian Goldfields Open champion Barry Hawkins.
Elsewhere in the last-32, last year's runner-up Ali Carter takes on Ben Woollaston while 2010 world champion Neil Robertson begins against Robert Milkins, who ended Jimmy White's hopes of a Crucible return in qualifying at the weekend.
Round one draw in full – all matches best of 19 frames (nine frames first session and remainder in second)
Ronnie O’Sullivan v Marcus Campbell (20th April 10am & 7pm)
Ali Carter v Ben Wollaston (22nd April 7pm & 23rd April 7pm)
Stuart Bingham v Sam Baird (24th April 7pm & 25th April 7pm)
John Higgins v Mark Davis (21st April 2.30pm & 22nd April 2.30pm)
Shaun Murphy v Martin Gould (20th April 2.30pm & 21st April 7pm)
Graeme Dott v Peter Ebdon April 10am & 22nd April 10am)
Matthew Stevens v Marco Fu (23rd April 10am & 24th April 2.30pm)
Judd Trump v Dominic Dale (23rd April 2.30pm & 24th April 10am)
Neil Robertson v Rob Milkins (24th April 2.30pm & 25th April 2.30pm)
Ricky Walden v Michael Holt (20th April 10am & 21st April 10am)
Mark Williams v Michael White (20th April 7pm & 21st April 2.30pm)
Stephen Maguire v Dechawat Poomjaeng (22nd April 2.30pm & 23rd April 2.30pm)
Mark Allen v Mark King (22nd April 10am & 7pm)
Ding Junhui v Alan McManus (23rd April 10am & 24th April 10am)
Barry Hawkins v Jack Lisowski (20th April 2.30pm & 21st April 7pm)
Mark Selby v Matt Selt (23rd April 7pm & 24th April 7pm)
- Sports & Recreation
- Mark Selby
- Ali Carter