The actress had signed up to appear opposite Cruise in the upcoming sci-fi film, but she was also offered the chance to take the lead in Kathryn Bigelow's new drama, which chronicles the real-life search for terrorist leader Osama bin Laden.
Chastain was unable to juggle both movies' schedules and eventually accepted the part in Zero Dark Thirty over Oblivion - and she is glad Cruise reacted well about her choice.
She tells Britain's GQ magazine, "When Kathryn cold-called me, asking whether I would be interested in this role, I was already working on another movie. I'd already signed up for it.
"Tom was actually very gracious about it. I wanted to do both but in the end I couldn't work it out."
Writer Mark Boal is delighted Chastain opted for Zero Dark Thirty, adding, "It's hugely flattering for Kathryn and myself. But from a business point of view, to make that shift happen was pretty challenging. When an actor you want in your film is already signed up with another studio - and with Tom Cruise? Those were really interesting (calls) to make, let me tell you. But Jessica was a no-brainer for us. We are very lucky to have got her."