The Star Trek actor will appear in at least four episodes, starting with a two-part Halloween-themed episode.
Quinto will star alongside Torchwood actor Teddy Sears as a gay couple who used to live in the house now owned by Dylan McDermott and Connie Britton's characters.
Quinto came out as a homosexual man last weekend and attributed his decision to the suicide of gay teenager Jamey Rodemeyer in September.
The two-part Halloween episode of American Horror Story will air on October 26 and November 2.
Watch the first clip of Zachary Quinto in American Horror Story below:
Watch the second clip, with more spoilers, below: