Chastain will have appeared in seven films before the end of the year. Her latest is the thriller, "The Debt," which also features Oscar-winner Helen Mirren.
The two worked together to synchronize their role. The actresses play the same person, an Israeli secret agent at different times in the character's life.
"We talked about Rachel's back story, what happened to her family, why she joined the Mossad, how she did it, and we talked about certain mannerisms that we may use and when in the film to use them," Chastain said.
Chastain said studying Mirren so their mannerisms could appear seamless could not be considered work.
"I'm a crazy Helen Mirren stalker, crazy stalker!" Chastain joked. "I love her so much. I got her book that had just like come out and I read her book and then I watched probably every single YouTube interview she had ever given."
Chastain is riding a wave of good jobs this year, including Terence Malick's "The Tree of Life," opposite Brad Pitt.
She also appears in "The Help," which has topped the box office three weeks in a row.
"I had so much fun making this film," Chastain said of "The Help." "We got to just hang out in Mississippi and eat all day long, and drink sweet tea and we just laughed. It was this wonderful summer camp experience.
"I'm so proud of all the performances in the movie and... that it's doing well in the box office makes me hope that Hollywood then wants to create more films where it's an ensemble of women, because it's one of the most wonderful experiences I've had making a film."
Next up for Chastain is "Take Shelter," a drama also starring Michel Shannon. It's slated for release at the end of September.
Later this fall, she will appear in films with co-stars that include Al Pacino and Ralph Fiennes.