In December 2007, he made a cameo appearance in the movie Walk Hard: The Dewey Cox Story, playing Buddy Holly.
In 2008, he began work on a film with former Missy Elliott protégée Brianna Perry, but the project was never released.
Muniz subsequently played the title role in the film Agent Cody Banks as well as its sequel, Agent Cody Banks 2: Destination London.
The first film opened in March 2003, and grossed $47 million; the sequel, which opened a year later, grossed $28 million.
He trained in martial arts for the films, and performed most of his own stunts.
He also commented that it was the point in his career where he should "make the transition from child actor to an adult actor or a respectable actor." Muniz provided the character voice of a zebra named Stripes, who wishes to become a racing equine, in the 2005 film Racing Stripes.
In 2012, he made a cameo appearance as himself in the second season of the comedy Don't Trust the B---- in Apartment 23. In 2006, he was also executive producer for the movie Choose Your Own Adventure: The Abominable Snowman.