The US singer will perform her new track 'Part of Me' on Saturday's (March 17) show.
Steve Jones and Alex Jones host the talent programme, which will also feature a performance from JLS with their Sport Relief single 'Proud'.
Eight celebrities will be dancing in the final, hoping to take over from James Thornton and Charlie Baker as the Let's Dance champions.
The full list of finalists and performances are below:
Terry Alderton – Tina Turner 'Proud Mary'
Tameka Empson and Laurie Brett – Lady GaGa and Beyonce ' Telephone'
Eddie 'The Eagle' Edwards – Austin Powers 'Soul Bossa Nova'
Miles Jupp – The Prodigy 'Firestarter'
Tyger Drew Honey and Dani Harmer – Bugsy Malone 'Fat Sam's Grand Slam'
Omid Djalili – Public Enemy 'Fight The Power'
Rowland Rivron – Fatboy Slim - 'Weapon Of Choice'
Fatima Whitbread and The Cuban Brothers – The Bee Gees - 'You Should Be Dancing'
Let's Dance For Sport Relief's finale airs on Saturday on BBC One and BBC One HD.
> Rowland Rivron, Fatima Whitbread in 'Let's Dance for Sport Relief' final