Music producer and television personality Simon Cowell is organizing the charity recording, which will also feature vocals by Mika, James Morrison, Rod Stewart, Leona Lewis, JLS, James Blunt and Joe McElderry, the BBC said.
The stars reportedly are taping their parts at different times and the song will be compiled by producer Steve Robson.
"I'm very honored to be asked to contribute to the single," Williams told the British broadcaster. "We can all do something to help the people of Haiti and I urge everyone to do what they can."
The BBC said the single's proceeds will be divided between the Helping Haiti fund and the Disasters Emergency Committee.
An estimated 200,000 people have died as the result of the Jan. 12 earthquake.
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