Parker will star in several episodes of the show's new season, TV Line reports.
Colin Hanks has already signed up to play Travis, an expert on ancient artifacts.
Parker's character Lisa is Travis's sister, but further details of the role have not yet been revealed.
Parker previously played Alma in Deadwood and starred in shows such as Swingtown and Shattered. She has appeared in movies including The Road and The Wicker Man.
Dexter's sixth season, which will air on Showtime later this year, will also feature appearances from Brea Grant, Billy Brown, Mos Def and Edward James Olmos.
Watch a teaser for the sixth season of Dexter below: