In 1982, Bell had a short uncredited scene in the Sydney Pollack film, Tootsie, playing a waiter at the Russian Tea Room. He worked on The Verdict (1982) for two weeks as a courtroom reporter in the trial.
In 1982 Bell landed his first speaking role in the last few moments of the drama Sophie's Choice, starring Meryl Streep. Bell moved to Los Angeles and was cast in his first feature film, Alan Parker's Mississippi Burning (1988), as a "tough,street smart, FBI agent". Bell played an assassin called "The Nordic Man" in another Pollack film, The Firm(1993). He went on to appear in an episode of the sitcom Seinfeld titled "The Old Man" playing a record store owner. He appeared in two episodes of NYPD Blue playing different characters; he played Donald Selness in a 1993 episode and Jerry the Artist in a 1996 episode.
In 1994, Bell played a hospital administrator in the second episode of the first season of ER and went on to appear in an episode of another medical drama Chicago Hope, playing a terminally ill inmate on death row. That same year, he portrayed the "Unabomber" in the made-for-television film Unabomber: The True Story. In 1997, Bell guest starred in an episode of La Femme Nikita and Nash Bridges. The following year, he guest starred in an episode of Stargate SG-1 and a two-part episode of Walker, Texas Ranger. He also appeared as villain Peter Kingsley during the second season of 24.
In 2004, Bell was cast as the nefarious Jigsaw Killer, an engineer who wants others to appreciate the value of life via twisted "games", in the horror film Saw. The low-budget film was a box office success, spawning six sequels: Saw II (2005), Saw III (2006), Saw IV (2007), Saw V (2008), Saw VI (2009), and Saw 3D (2010). He provided his voice for the Jigsaw character in the Saw video game (2009) and its sequel, Saw II: Flesh & Blood (2010), to which he provided his likeness. Even though Bell spent three weeks lying on a floor and had very few lines, his role was pivotal to the first film. For his role as "Jigsaw", Bell received MTV Movie Awards nominations in 2006 and 2007 for "Best Villain", won "Best Butcher" in the Fuse/Fangoria Chainsaw Awards and was given the "Best Villain in a Film Series" title at the 2010 Chiller-Eyegore Awards. Although he considers his role in Saw to have been "a great blessing", he hopes to soon have the opportunity to be cast against type. In 2016, he starred as hermit Yo Ling on the soap opera Days of Our Lives, who is John Black's long last father.