The Rocket is among the England team skippered by pop mega-star Williams which will take on a rest-of-the-world outfit captained by Gordon Ramsey.
Soccer Aid is raising funds for UNICEF's global health, education and protection work with vulnerable children.
Ant and Dec will present daily shows on ITV, starting at 9pm on Monday, following the teams as they spend the week training for a place in the starting line-up for the big match at Old Trafford next Saturday.
Two-times snooker world champion O'Sullivan was a promising footballer in his teenage years and had a trial with Tottenham Hotspur, though he is now an Arsenal fan and will be cheering the Gunners on in the Champions league final tonight.
His team-mates in Sport Aid will include Jamie Theakston, singer David Gray, Angus Deayton and football legends Paul Gascoigne and John Barnes.
Lining up for the rest-of-the-world are the likes of Patrick Kielty, David Campese, Ruud Gullit, David Ginola and Ginafranco Zola.
Chigwell's O'Sullivan, 30, said: "It's for a great cause and it should be a lot of fun so I'm looking forward to it."
Wed 05/17/06, 4:19 am EST