In his short career, Simpson has had many featured roles, starting with his first appearance in Loser. Since then, he has had featured roles in 24, Herbie Fully Loaded, Stay Alive, Itty Bitty Titty Committee, Zodiac, The Invention of Lying, Date Night, It's Always Sunny in Philadelphia and Psych. He currently stars in the series Breakout Kings. He is also well known to fans of Late Show with David Letterman as Lyle the intern.