Marnò played the title role in the 2008 film The Stoning of Soraya M., about a woman whose husband falsely accuses her of adultery, resulting in her death by stoning.
In addition she has had roles in a number of television series including The Paul Reiser Show, The Glades, Hung, The Mentalist, Bones, The Unit, Medium, K-ville and Standoff. Marnò also appeared in the Untitled John Wells Medical Drama Pilot, which was not aired. She also stars in Ana Lily Amirpour's directorial debut, A Girl Walks Home Alone at Night, produced by Elijah Wood, under his company, The Woodshed.
Marnò also directs and writes screenplays. Her first feature length screenplay, When the Lights Went Out, was a quarter finalist for the Nicholl Fellowship, a finalist at the Nantucket Screenwriter's Colony, Sundance Screenwriter's Lab, and won third prize at the Cinequest Film Festival Screenwriting Competition. She has adapted When the Lights Went Out as a play and it received its first production at New York Stage & Film in July 2013 starring Laura Innes from ER.
Marnò's short film, Incoming, which she wrote and directed, was accepted to the Noor Film Festival, LA SHORTS FEST, the Asians on Film Festival, and the DC Asian Pacific American Film Festival.
- 2007: Charlie Wilson's War
- 2008: August as Ashley
- 2008: Traitor as Leyla
- 2008: The Stoning of Soraya M. as Soraya M.
*Nominated - Satellite Award for Best Supporting Actress - Motion Picture
- 2009: StereoLife as Gwendolyn Leeds
- 2014: House of Cards as Ayla Sayyad