His addition to the CW drama was announced this afternoon during the Television Critics Association's summer press tour.
Henriksen joins the ranks of the Justice Society of America, which already includes Patrick J. Adams as Hourman, Maisie Richardson-Sellers as Vixen, Matthew MacCaull as Commander Steel and Sarah Grey as Star Girl.
Doctor Mid-Nite is also part of the classic superhero team, but no casting has been revealed.
The son of the Golden Age Green Lantern, Obsidian was introduced in 1983's "All-Star Squadron" #25, and joined a modern incarnation of the Justice Society in 2007. He can merge with his own shadow, allowing him to fly and pass through solid objects, and possess the shadows of others.
Henriksen's lengthy list of film and television credits is dotted with memorable sci-fi and horror roles, from "The Terminator" and the "Alien" franchise to "Near Dark" and "Millennium."
"DC's Legends of Tomorrow" returns for its 13-episode second season Oct. 13 on The CW.