The baker, 33, will make history as one half of the first ever all-male partnership in the BBC series.
The news was revealed by Matt Lucas on BBC Radio 2 on Thursday morning.
Whaite — who revealed in 2017 that he was engaged to his designer partner Paul Atkins — said he was “born to be on the dancefloor”.
Sharing his news on Instagram, he said he was filled with "uncontrollable excitement" about being on the show.
He wrote: "I’ve been wearing sequins, wigs and jazzy clothes since I was in the womb (winner of the best dressed foetus award, 1989), but even that hasn’t prepared me for the uncontrollable excitement that I’m filled with when I say: I’m part of the 2021 @bbcstrictly line-up.
"Oh, and I’m going to be dancing with another bloke as the first all-male pairing."
Whaite, who won Bake Off in 2012, joins Tom Fletcher, Robert Webb and AJ Odudu in the new series of the ballroom contest.
A raft of other celebs are set to be announced in the coming days.
The show was cut short last year amid the coronavirus pandemic, from 13 weeks to just nine. This led to the cancellation of both the popular Halloween Week and the annual trip to Blackpool's famous Tower Ballroom.
Bosses have promised fans a full-length series this year but said the show will not be able to return to Blackpool.
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