The former Take That singer will join Matt Lucas and David Walliams in one of two exclusive skits, to be shown on Red Nose Day on Friday March 13.
Robbie will appear as Candy Marie-Candy, a friend of Ellie Grace, played by Matt. Ellie invites Candy to a sleepover, where the pair play a game of ‘I love you more…’ with hilarious results.
On filming the sketch for Comic Relief, Robbie said: “It’s hard to say no when asked to take part in a Little Britain sketch for Comic Relief.
“But I have to admit that dressing up as a small American child in a pretty dress made it all the more appealing.”
David said of Robbie’s performance: “Robbie was absolutely brilliant in the Ellie Grace sketch. He could be a comedian full time if he wanted to.
“And we have found that the best way to tempt him back into the spotlight is by putting him in a dress!”
Comedienne Catherine Tate will appear in the other sketch as the ruthless boss of Little Britain favourite Carol Beer, played by David.
Catch both sketches on Comic Relief’s night of comedy on Friday March 13 from 7pm on BBC1.