In the movie, Weisz plays real-life whistleblower and Bosnian peacekeeper Kathryn Bolkovac, who brings to light a child sex-slave scandal allegedly being covered up by the United Nations.
The actress was first offered the part in 2006, when she was expecting son Henry with her then-fiance, Black Swan director Darren Aronofsky - but the star wasn't mentally or physically prepared to tackle the topic and rejected the job.
Appearing on U.S. breakfast show Today on Wednesday (27Jul11), she says, "I did read the script in 2006; I was pregnant with my son. It was too (much), I couldn't cope with it at that moment.
"But the strange thing was I just never forgot about it. And about two years ago I called up the producer, who I knew, and I said, 'Remember that script The Whistleblower? Does it still exist?' And she said, 'Yes,' and so it kind of came back. It just stayed with me."
And the Oscar-winning star is glad she stuck with her gut because the project has been especially rewarding: "I'm really excited for people to see it... because it's based on the true story about an ordinary woman who did an extraordinary thing and I love stories like that."