The 34-year-old actress - who was played Jessica Brody in the popular American drama for which she received an Emmy nomination - will star as Karen Walker in director Paul Feig's forthcoming film.
Baccarin joins an A-List cast in the story which centres on 'The Heat' star Melissa McCarthy whose is a CIA analyst that goes into the field for the first time.
Other stars in the line up include Jason Statham, Rose Byrne, Jude Law, Bobby Cannavale, Miranda Hart, and Nia Long.
Feig is also producing for his Feigco Entertainment banner alongside Peter Chernin, Jenno Topping, and Jessie Henderson.
'Spy' has been slated for a Memorial Day 2015 release and filming has already begun in Europe.
Meanwhile, Baccarin - who is married to film producer and director Austin Chick - will next hit the big screen in 'Back in the Day' and lent her voice to the character of Talia al Ghul in 'Son of Batman'.