Walsh will be joined by comics Paddy McGuinness and Jason Manford on the charity celebrity talent contest.
Steve Jones and Claudia Winkleman return for a second series of the dance show on Saturday night. Katy Brand, Rufus Hound, Linda Robson, Lesley Joseph and snooker star Willie Thorne were previously confirmed as contestants.
Further stars revealed to be taking part in the competition include Holby City's Rosie Marcel and Luke Roberts and Casualty stars Charles Dale, Tony Marshall and Ben Turner.
Olympians Mark Foster, Iwan Thomas, Leon Taylor, Dalton Grant, Heather Fell and Jamie Baulch have been confirmed, while TV duo Sam and Mark will also perform on the dancefloor.
News presenters Matt Barbet, Ellie Crisell and Louise Minchin and darts legends Bobby George and Tony O'Shea will also take part.
Let's Dance for Sport Relief airs on Saturday at 6.30pm on BBC One.