Somerhalder is set to play Damon, a smug vampire who can go from playful to evil in a split second.
Thesp’s credits also include “Tell Me You Love Me.”
Also joining the cast are Zach Roerig (“Friday Night Lights”), who will play the jock Matt, and Kayla Ewell (“Entourage”), who will play Matt’s sister.
Previously announced cast includes Nina Dobrev and Steven R. McQueen.
“Vampire Diaries,” based on a series of books from Alloy Entertainment, centers on a woman who falls for two vampire brothers – one good and one evil.
Warner Bros. TV is behind the project, along with Alloy and Outerbanks Ent.