The Girls Aloud singer will star alongside Mock the Week comic Hugh Dennis, Extras actress Ashley Jensen and rapper Ashley Walters in the Vertigo film.
The 30-year-old's only previous big screen role was a cameo in children's show spinoff Horrid Henry: The Movie alongside Theo Stevenson, who will also feature in the picture.
"I am thrilled to be joining the cast of All Stars," she said. "I have worked with Theo before on Horrid Henry and he is a huge talent.
"I loved the script as soon as I read it. It is a heart-warming family film that will put a huge smile on your face."
Producers Allan Niblo and James Richardson added: "We are delighted to have Kimberley for the role of Trish, she is a brilliant actress with an electric screen presence. She joins an amazing cast in what will be an exciting film."
Pictured: Walsh's other co-stars Ashley Jensen and Ashley Walters
Ben Gregor makes his feature directorial debut based on the original script by Paul Gerstenberger. The story follows a group of misfits with a dream to organise a show to save their youth centre.
Walsh recently finished her sell-out Shrek the Musical tour as Princess Fiona. She replaced Amanda Holden in September.
The star is expected to reunite with Girl's Aloud bandmates Cheryl Cole, Nadine Coyle, Sarah Harding and Nicola Roberts for the girl group's tenth anniversary later this year.