Morrissey is to play The Governor, a character from the Robert Kirkman graphic novel on which the series is based. He is the leader of Woodbury, a small settlement of survivors, and will become the chief antagonist for Rick Grimes, played by Andrew Lincoln, and his group, the cable network said.
The 16-episode third season is to begin production this spring in Atlanta.
A BAFTA Award nominee, Morrissey has appeared in many acclaimed British series, including "State of Play," "Meadowlands," "The Deal" and "Blackpool." He is also known for his leading roles in feature films such as "The Reaping," "The Other Boleyn Girl," "Centurion," "The Water Horse," "Nowhere Boy" and "Blitz."
Season 2 of "The Walking Dead" airs Sundays on AMC.