Knight of Cups already stars Christian Bale and Natalie Portman, who is set to appear in another Malick film, but Pinto was not announced to have joined the project until she was spotted on the Los Angeles set with Bale, reports Indiewire.
Pinto joins other unannounced stars who have been seen on the set of the film, including The Hunger Games' Wes Bentley and Imogen Poots.
Knight of Cups, which also stars Cate Blanchett and Isabel Lucas, follows a man (Bale) as he searches for love and truth.
After Knight of Cups, Malick will shoot another film that was formerly called Lawless.
The media-shy Tree of Life director was accidentally caught on film by TMZ recently.
Watch the trailer for The Tree of Life below: