The 35-year-old star's character has yet to be confirmed, while Walliams will play Burt, reported Contactmusic.
Ratburger revolves around the story of a little girl called Zoe who struggles to keep her pet rat out of the hands of evil Burt from Burt Burgers, who's eager to serve the pet up for dinner.
Smith has previously teamed up with Walliams in the 2012 adaptation of his novel, 'Mr Stink' and in an episode of "Walliams and Friends".
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