The 22-year-old star of "Ice Princess," "Aquamarine," "Nancy Drew," "The Winning Season" and "Scream 4" would play a self-involved party girl named Madison in "American Horror Story: Coven," the television news website said.
No other details regarding the character or her story line were immediately available.
The show features a repertory ensemble, which also includes Jessica Lange, Sarah Paulson, Lily Rabe, Frances Conroy, Taissa Farmiga and Evan Peters, Roberts' real-life boyfriend.
Every season follows a new set of characters in different times and places than the previous season.
Season 1 was about ghosts, while the second season was about the residents of an insane asylum. Season 3 will be about witches and will include appearances by Kathy Bates, Angela Bassett, Patti LuPone and Gabourey Sidibe.