The musician is making his cover of Stevie Wonder's "You and I" available to download for free and hopes fans will make a donation to the Royal Wedding Charity Fund. Michael debuted the song Friday on CNN's "Piers Morgan Tonight."
Michael said he spent about two days in the studio crafting the cover and that Wonder provided clearance to distribute the track for free.
"The idea came to me last week, about a week ago, that I should express my happiness at the marriage publicly," Michael told Morgan.
Michael was a friend of William's mother, the late Princess Diana, but he 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." The former Wham! singer spent a month in jail last year for crashing his Range Rover while under the influence of drugs.