The comedian is the last contestant to be confirmed for this year's lineup and will compete in the third and final heat on Saturday.
Lee will be joined by previously announced comedians Adrian Edmondson, Marcus Brigstocke and Lee Nelson.
Caroline Flack and Joe Swash will also compete along with popstars Chesney Hawkes, Toyah Wilcox, Clare Grogan and Limahl.
The hopefuls will be judged by John Bishop, Felix Dexter and Jo Brand, while Jessie J and The Wanted will perform in the studio.
James Thornton and Charlie Baker, Noel Fielding, Russell Kane and Katie Price have already made it through to the final.
Let's Dance For Comic Relief airs on Saturday at 6.40pm on BBC One.