“Mad Men’s” Jared Harris has been cast as the villainous Professor Moriarty in Warner Bros.’ “Sherlock Holmes” sequel.

The studio had been considering a number of thesps, including Daniel Day Lewis, to play the arch nemesis of the iconic British sleuth, before landing on Harris, who has history of portraying slithery characters in Fox’s “Fringe” and FX’s “The Riches.” Brad Pitt was not in the running, despite several reports.

Studio confirmed the Harris’ casting, first reported on LatinoReview.com. His credits also include Paramount’s “The Curious Case of Benjamin Button.”

The Moriarty character briefly appeared in the franchise’s first outing last year, but his face was never revealed. The character will serve as the main villain in “Sherlock Holmes 2.”

Robert Downey Jr. returns as Holmes, pairing up with Jude Law again as Dr. John Watson.

Casting is well underway on the next installment, with “The Girl with the Dragon Tattoo’s” Noomi Rapace playing the female lead in her first English role, and Stephen Fry recently cast as Holmes’ brother.

Warner Bros. has set a Dec. 16, 2011, release date for “Sherlock Holmes 2” with Guy Ritchie returning as director along with producers including Dan Lin, Joel Silver, Susan Downey and Lionel Wigram.

Kieran and Michele Mulroney penned the script.