The 80s-set drama, chronicles the rise of the HIV/AIDS crisis in New York in the 1980s.
Mark Ruffalo was already signed up to take the of Ned Weeks in the movie, which Julia will play wheel-chair bound doctor Emma Brookner, a role for which Ellen Barkin won a Tony Award, reports Contactmusic.
Alec Baldwin will portray Mark's character's brother, a lawyer who is struggling to deal with his sibling's sexuality.
It will be the second time Ryan and Julia have worked together following the success of 'Eat Pray Love'. (ANI)