The Artist actor will portray Dr. Arden on the second season for a ten-episode arc, reports Deadline.
Cromwell's Dr. Arden works in an East Coast institution for the criminally insane run by Jessica Lange's character.
Creator Ryan Murphy previously said that the second season will have new cast members and a new location.
"It's a completely different world and has nothing to do with season one," he explained. "There's not a mention of season one. The second season is set in a completely different time period."
American Horror Story's second season will focus on Lange, who was a reoccurring character on the show's first season as Constance Langdon.
Watch the trailer of American Horror Story's first trailer below: