Clemenson starred in the film "United 93" as Tom Burnett, one of the victims of the 9/11 hijacking of the flight that crashed in rural Pennsylvania after a passenger revolt. He also had a recurring role on "Veronica Mars" as Abel Koontz. In total, Clemenson appeared in three episodes of the show: "Like a Virgin", "Mars vs. Mars", and "Rat Saw God". Clemenson also has appeared in a season 6 episode of "NCIS", "Dead Reckoning". He also appeared in two season 2 episodes of "The Mentalist". He also played Jimmy Masterson on the 3rd episode of "Memphis Beat", "Love Me Tender."