McDermott, best known for his starring role in TV's "The Practice," and the surnameless actress helped bring Eve Ensler's play to the stage for the first time, Playbill.com reported.
The play follows Portia, in the role of a psychologist Colonel, as she treats a traumatized former military interrogator played by McDermott, who marked his third collaboration with Ensler.
The 44-year-old actor previously joined forces with Ensler in "Floating Rhoda and the Glue Man" and "Scooncat," Playbill said.
The Impact Festival runs through Oct. 22 and will feature performances from Marisa Tomei, Richard Dreyfus, Jeff Goldblum, Charles Grodin, Steve Earle, David Strathairn, Samantha Power and Bob Balaban.
Swim Week Miami Beach 2014 [PHOTOS]