UPDATE: Party Down alumna Lizzy Caplan has just closed her deal, and she is now set to play Virginia Johnson opposite Sheen.

EXCLUSIVE: Michael Sheen, best known for portraying Tony Blair and David Frost in films, will get to play another famous person, this time on a TV series. In his first regular series role, the British actor is set to star in Showtime’s drama pilot Masters of Sex, portraying 1960s human sexuality pioneer William Masters. In addition to starring, Sheen and his manager Tammy Rosen will serve as producers on the show. The project, written by Michelle Ashford (The Pacific) and directed by John Madden (Shakespeare In Love), is an adaptation of Thomas Maier’s book Masters of Sex: The Life And Times Of William Masters And Virginia Johnson, The Couple Who Taught America How To Love. It chronicles the lives, romance and pop culture trajectory of Masters (Sheen) and Johnson, whose research touched off the sexual revolution. Sheen replaces another Brit, Paul Bettany, who was originally attached but parted ways with the producers last month. With Sheen set, the focus will now shift to casting the Johnson role, for which Lizzy Caplan has been in negotiations. Masters Of Sex is produced by Sony Pictures TV, with Judith Verno and Timberman/Beverly Prods’ Sarah Timberman and Carl Beverly executive producing. Production on the pilot is slated to begin in March in New York. Sheen is the latest feature actor tapped as the lead of a Showtime series follwoing the recent castings of Claire Danes in Homeland, Don Cheadle in House Of Lies, and Liev Schreiber in the pilot Ray Donovan.

Sheen portrayed former British Prime Minister Tony Blair in the feature The Queen and two TV movies that aired on HBO, The Special Relationship, which earned Sheen an Emmy nomination, and The Deal, originally commissioned by U.K. Channel 4. He played leading British interviewer David Frost in Frost/Nixon. Sheen, repped by ICM; Sanders, Armstrong, Caserta Management; and UK’s Roxane Vacca, was recently seen in Beautiful Boy and the Oscar-nominated Midnight in Paris. He is set to reprise his role as Aro in The Twilight Saga: Breaking Dawn – Part 2. Sheen’s only U.S. series appearance was a four-episode arc on 30 Rock in 2002.

CAA-repped Caplan is currently doing a multi-episode arc on Fox’s New Girl. Her series credits also include True Blood, The Class, Family Guy and Freaks and Geeks. On the film side, she was at Sundance with 2 comedies, which premiered at the festival – Bachelorette and Save the Date.