Remar has spent the majority of his film career playing villains. He is known for his roles as the aggressively sexual and violent character Ajax in the 1979 cult film The Warriors and as the murdering sociopath Albert Ganz in the 1982 hit 48 Hrs. both directed by Walter Hill. Remar played real-life '30s-era gangster Dutch Schultz in the 1984 film The Cotton Club. He starred in the 1980 film Windwalker as the young Windwalker. He also portrayed a gay man in the 1980 film Cruising. In 1996, he played Quill, one of the main villains in The Phantom.
Remar was cast as Corporal Hicks in the 1986 science-fiction/horror film Aliens (co-produced by Walter Hill), but was replaced by Michael Biehn shortly after filming began due to "creative differences" with director James Cameron. (At least one piece of footage featuring Remar made it into the final version of the film, when the Marines enter the processing station and the camera tilts down from the Alien nest, though Remar is not seen in close-up.)
Other notable films include Drugstore Cowboy, Fear X, Boys on the Side, Hellraiser: Inferno, The Quest, Wedlock, Tales from the Darkside: The Movie, Blade: Trinity, 2 Fast 2 Furious, The Girl Next Door and in 1998 he played the policeman that kept following the woman around in Psycho, he was also the star of the 1986 film Quiet Cool. He portrayed the character of Raiden in Mortal Kombat: Annihilation, the sequel to the 1995 movie adaptation of Mortal Kombat, taking over the role from Cristopher Lambert. He then followed this with a role in the 1996 direct-to-video science fiction movie Robo Warriors.
Remar's guest appearances range from Pineapple Express, Miami Vice, Hill Street Blues, Sex and the City, Third Watch, Justice League Unlimited and Battlestar Galactica, as well as appearing as a possessed mental patient in the X-Files ninth season episode "Daemonicus". He was in the miniseries The Grid (2004) as Hudson "Hud", the love interest of Julianna Margulies' character. He starred as Tiny Bellows on the short-lived television series, The Huntress. He had a recurring guest role in the television series Jericho on CBS.
In 2010, he did a guest role as Giuseppe Salvatore in The Vampire Diaries. Remar was a recurring character on FlashForward. He played James Irskan, who is a General for a black-ops military contractor.
He also voiced Vilgax in Ben 10: Alien Force.
- James Remar had a role in the 2009 horror movie The Unborn which also had actor C.S. Lee who portrayed Vince Masuka in Dexter.