The late "Black Panther" star, who served as a producer on the thriller, campaigned to recruit the Brit as his co-star and then took a pay cut to make sure she was properly compensated.
"He produced 21 Bridges, and had been really active in trying to get me to do it," the "American Sniper" actress tells Empire. "He was a fan of my work, which was thrilling, because it was reciprocated from me to him, tenfold."
"So he approached me to do it, he offered me this film, and it was at a time when I really didn't want to work anymore. I'd been working non-stop and I was exhausted, but then I wanted to work with him."
But her initial salary demand was turned down by movie bosses, prompting Chadwick to step in.
"I think it's a testament to who he was," she adds. "This was a pretty big budget film, and I know that everybody understands about the pay disparity in Hollywood, but I asked for a number that the studio wouldn't get to. And because I was hesitant to go back to work and my daughter was starting school and it was an inconvenient time, I said, 'I'll do it if I'm compensated in the right way'. And Chadwick ended up donating some of his salary to get me to the number that I had asked for. He said that that was what I deserved to be paid."
"It was about the most astounding thing that I've experienced," she continues. "That kind of thing just doesn't happen. He said, 'You're getting paid what you deserve, and what you're worth.'
"It's just unfathomable to imagine another man in that town (Hollywood) behaving that graciously or respectfully. In the aftermath of this I've told other male actor friends of mine that story and they all go very very quiet and go home and probably have to sit and think about things for a while. But there was no showiness. It was, 'Of course I'll get you to that number, because that's what you should be paid.' "