The series will air its final season on FX, from September 9 in the US, according to Hollywood Reporter.
Warner has been tapped to play a member of the Grim Bastards called Sticky.
The 43-year-old actor is scheduled to appear in the show's seventh season opener.
Warner joins this season's guest stars, Courtney Love and Marilyn Manson.
He recently appeared in 'Major Crimes' and 'The Michael J Fox Show'.