The Hollywood Reporter confirmed Friday the 33-year-old actress will star in the new HBO limited series.
Maslany joins Matthew Rhys, who will portray the titular defense attorney. The series is set in 1932 Los Angeles and serves as origin story for Mason, who begins as a down-on-his-luck private investigator.
Maslany will play Sister Alice, an influential nun. The character is the leader of the Radiant Assembly of God and preaches three sermons a day to her congregation and a radio audience.Perry Mason is based on the character from author Erle Stanley Gardner. CBS previously adapted the detective stories as a TV series starring Raymond Burr that aired from 1957 to 1966.
Variety said the new Perry Mason revolves around a child kidnapping case. Mason pursues the truth, discovering a fractured city and a possible pathway to redemption for himself.
Robert Downey, Jr., and Susan Downey will executive produce the series with Amanda Burrell and Joe Horacek. Rolin Jones and Ron Fitzgerald will serve as co-showrunners, with Tim Van Patten as director.
Maslany is known for the BBC America series Orphan Black. She has since appeared on Drunk History and voiced characters in Trollhunters, Animals. and 3Below: Tales of Arcadia.