See Jessica Chastain's Transformation for 'Tammy Faye' Movie: 'The Best Part I've Ever Played'

Jessica Chastain heads into awards season as a top contender for her latest movie.

In a featurette about Chastain's upcoming movie The Eyes of Tammy Faye, exclusive to PEOPLE, the actress is seen undergoing a total transformation into renowned televangelist Tammy Faye Bakker.

"I thought she was a thief, that she and [ex-husband] Jim Bakker had stolen millions of dollars," Chastain says in the featurette, above. "When I watched the documentary, I got to know her as someone who believed that everyone is deserving of love without judgment."

Chastain, already a two-time Oscar nominee, underwent a deep physical transformation to portray Bakker.

"I had hours and hours of footage to just watch of her," Chastain says. "She speaks in a Minnesota accent and that's what makes her so sweet and folksy. So working on that accent was a huge thing."

Her costar, Cherry Jones, says Chastain was "encased in latex, wigs, pregnancy pads, nails out to here" for her performance.

"I don't even know how to describe what it must feel like and then to have to be this woman who people still remember and remember well," Jones adds.

For Chastain, it was simply her job to show Bakker "as she was and not how people want to remember her."

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"It was the best part I've ever played and it was great fun to kind of sink my teeth into it," the actress says.

Directed by Michael Showalter (The Lovebirds) and written by Abe Sylvia (The Producers), the film follows the story of Tammy Faye Bakker as she and her husband, Jim Bakker, rise from humble beginnings to create the world's largest religious broadcasting network and theme park.

As the two gain success, their empire crumbles under the pressure of financial mishandlings, scheming rivals and scandal.

The film also stars Andrew Garfield as Jim Bakker, Fredric Lehne, Louis Cancelmi, Sam Jaeger, Gabriel Olds, Mark Wystrach and Vincent D'Onofrio.

The Eyes of Tammy Faye is in theaters on Sept. 17.