Poston began his career in the cast of the Broadway Musical Chitty Chitty Bang Bang, acting in over 300 performances. In 2003, he had a small part playing a young main characters in the film Girls Will Be Girls. Poston played in the 2007 film Walk Hard: The Dewey Cox Story and he played Tommy Huff in the 2008 film Step Brothers with Will Ferrell and John C. Reilly. He plays Trevor in Disneys Kickin It.