Thomas will play a recurring character named Jason Hood, reports Deadline.
Banshee is the new Cinemax series produced by Alan Ball, who is stepping down as a showrunner on True Blood after the fifth season.
Banshee follows an ex-convict and master thief (Anthony Starr), who flees Pennsylvanian town Banshee as he is hunted down by gangsters he betrayed.
Demetrius Grosse recently joined the cast as Emmet Yawners, a college football player turned police deputy.
The 10-part series also features Odette Annable, Matt Servitto, Trieste Dunn and Daniel Ross Owens.
Thomas is a relative newcomer, having appeared in three series - House, Fringe and The Client List - and the television movie Locke & Key.
Watch a bonus scene of True Blood below: