While still in film school, Kinberg sold a pitch to Warner Brothers, then went on to write scripts for Disney, Sony, and DreamWorks, working with Steven Spielberg and Jerry Bruckheimer, among others. After finishing school, Kinberg moved to Hollywood, where his first screenwriting credit was a sequel to the hit action film XXX (2002), XXX: State of the Union (2005). His next screenwriting venture was the screenplay for Mr. & Mrs. Smith, directed by Doug Liman and starring Brad Pitt and Angelina Jolie. The script began as Kinberg's thesis project for film school. Kinberg also wrote the pilot episode for a television adaptation of Mr. & Mrs. Smith for ABC TV. He also appears in the movie, in a scene with Brad Pitt.