Papajohn got his start in acting while he was a student at Louisiana State University. Already an athlete, he was hired to be a stunt performer in the film Everybody's All-American which was being filmed on the campus of LSU and featured football action sequences filmed during LSU football games in Tiger Stadium. From there he moved on to being a stunt performer in films such as Money Talks and Starship Troopers and acting in films like Predator 2, For Love of the Game, where he plays New York Yankees slugger Sam Tuttle, and Spider-Man and Spider-Man 3, in which he plays Dennis Carradine, the thief that was thought to have killed Uncle Ben; Papajohn also makes a cameo appearance as a different character in the film series' reboot, The Amazing Spider-Man. He has also starred in Terminator 3: Rise of the Machines, Transformers: Revenge of the Fallen, Terminator Salvation, Land of the Lost, and G-Force in 2009.