In the Showtime series about a woman grappling with Dissociative Identity Disorder, Izzard will play a brilliant psychology professor skeptical about the disease. However, his growing fascination with Tara (Toni Collette) will lead him to explore the condition further.
The role will mark Izzard's return to American TV following his work on the short-lived 2007 FX drama The Riches. Izzard, 48, recently appeared on another Showtime original series, The Green Room with Paul Provenza.
Production on the third season of United States of Tara begins next month for a premiere in 2011.