Whoopi Goldberg committed to 'Till' because she was "interested" in the film.
The 66-year-old actress both stars in and produces the movie about Emmett Till – a 14-year-old boy who was lynched in Mississippi in 1955 for whistling at a white woman - and revealed that it was a passion project for her.
Speaking to Collider, Whoopi said: "I've only (ever) wanted to do stuff I'm interested in and stuff that I thought was interesting. It doesn't necessarily have to be interesting to other people.
"It only has to really interest me, that's always been the same. So getting to do this was a gift because this was not my plan."
Whoopi, who plays Emmett's grandmother Alma Carthan in the film, revealed that her role in the movie has changed over time.
The 'Sister Act' star said: "At one point I was going to act, but it was years and years and years ago. By the time we got it, I've evolved into grandma."
The project is based on more than two decades of research by Keith Beauchamp and Whoopi explained that she wanted family relationships to be at the centre of the story.
She said: "The story has always been very crystal clear because, of course, we had Keith (Beauchamp), who really is the bones of the project because this is something that he's been a part of forever. He made the documentary that reopened the case.
"This relationship between mother and son was always a priority. This was when Barbara Broccoli and Fred Zollo and I and Keith sat down, that was always the piece that we felt people needed to get.
"They needed to understand these are normal people. These are people who lived in Chicago, like your grandmother, your cousin, your uncle."