21-year-old Hemsworth, brother of "Thor" star Chris, will be the youngest cast member in the sequel. He will portray a sniper.
The 6'3" tall Aussie actor joins a cast of action legends with the confirmed list currently including Sylvester Stallone, Chuck Norris, Jean-Claude Van Damme, Arnold Schwarzenegger, Bruce Willis, Jason Statham, Dolph Lundgren, Jet Li, Mickey Rourke, Terry Crews, and Randy Couture.
New cast members include Hemsworth as well as Jean-Claude Van Damme and Chuck Norris,No plot details have been released yet.
The 2010 original centered on a group of mercenaries, led by Stallone, that are hired to remove a Latin American dictator from power.
It grossed over $275 million worldwide.
Hemsworth, who was last seen opposite Miley Cyrus in "The Last Song," will be seen opposite Jennifer Lawrence in "The Hunger Games."
The film is set to start production in Bulgaria next month.
Simon West is directing and Lionsgate will distribute the film.