The pooch, who won Britain's Got Talent in 2012 with partner Ashleigh, will lead a live-action family adventure film to be directed by Horrid Henry's Nick Moore.
Walliams, who was on the BGT judging panel when Ashleigh and Pudsey were crowned winners, said: "I am thrilled to be providing the voice of Pudsey. I have been coming up with different voices for him ever since that first audition."
Pudsey: The Movie will follow the titular dog and his siblings Molly (Izzy Meikle-Smith), George (Spike White) and Tommy (Malachy Knights) as they move to the village of Chuffington-on-Sea with their mother Gail (Jessica Hynes).
The gang stumble across an evil plan from their landlord Mr Thorne (John Sessions) and his cat Faustus and must set out to save the village.
Luke Neal and Luke Tittensor round out the supporting cast for Pudsey: The Movie, which began production on September 1 in the south of England.
The film will be released in the UK on May 2014.
Watch Ashleigh and Pudsey perform on Britain's Got Talent below: