Harrelson has joined the production to portray a henchman, Variety reported.
The film is a reunion for Harrelson and director Ruben Fleischer, who previously worked on 2009's Zombieland. Venom started filming in October with rumors of Harrelson joining the comic book film popping up off-and-on ever since.
The central character is a mainstay in Marvel's Spider-Man comics who first appeared as a villain before becoming an antihero. Venom is born after an alien symbiote bonds with photographer Eddie Brock, who is then gifted with powers similar to those of Spider-Man, along with other abilities. Venom was first portrayed in film by Topher Grace in 2007's Spider-Man 3.
Sony has stated that actor Tom Holland's Spider-Man, who is a part of Disney's Marvel cinematic universe, will not appear in Venom or the studio's second spinoff featuring female characters Black Cat and Silver Sable.