Pitt produced the Steve MCQueen film, in which Ejiofor plays the role of Solomon Northup, a free black man from New York who is abducted and sold into slavery, and the British actor is adamant the film would not have been completed without Pitt's expertise.
He tells E!, "I think the truth is we wouldn't have been able to make this film without Brad Pitt, because of what he brings... So him coming on board and him being a producer made, I think, the complete difference to make the film.
"It just goes to show what an individual could do when they have that kind of reach and they're prepared to use it to support filmmakers. I'm deeply grateful to him for allowing this film to be made."
The Fight Club star also makes a brief appearance onscreen as a Canadian abolitionist. The pre-Civil War film also stars Michael Fassbender as a plantation owner and is due for release later this year (13).