He began his career as a young child, making several guest appearances on popular TV shows before being cast as Owen Salinger on Party of Five, a role he held for two years.
During this period, he also starred in the made-for-television films Evolution's Child and the Disney Channel production Phantom of the Megaplex.
He was subsequently cast as one of twelve children in the family comedy Cheaper by the Dozen, which was released in December 2003 and became a box office success, gaining Smith renown with pre-teen audiences.
In 2004, he had a minor role in the film Troy and appeared on the television series Without a Trace.
He went on to reprise his role of Jake Baker in Cheaper by the Dozen 2, which was released in December 2005 and performed fairly well at the box office.