The Canadian actress became a household name following her roles in HBO drama "The Newsroom" and critically-acclaimed films such as "Milk" and "Scott Pilgrim vs. The World".
It is not yet clear what she will play in 'AHS', reported Screen Rant.
Series veterans Evan Peters and Sarah Paulson are set to return for the latest season.
Colton Haynes and Billie Lourd are among the other new faces making their "AHS" debut.
"American Horror Story" season 7 is expected to debut later this year.
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