The musician is making the track available to download for free, but hopes fans will make a donation to the Royal Wedding Charity Fund.
He has been teasing fans on Twitter about his choice of song, which he plans to reveal Friday on Piers Morgan's CNN show.
The former /*Wham!*/ singer, whose solo hits include "Faith" and "Freedom," spent a month in jail last year for crashing his Range Rover while under the influence of drugs.
Michael was a friend of William's mother, the late /*Princess Diana,*/ but said he wasn't expecting to attend the April 29 wedding. He tweeted that the couple should be "surrounded by people they love, not dodgy ex-con pop stars."
