The 45-year-old actress plays a woman betrayed by her husband in her new film, The Tribes of Palos Verdes, which she also executive produced.
"It was just really exciting getting to be a part of getting this movie made," Garner told ET at the Hamptons International Film Festival on Friday. "It's one of those tiny little movies that's an engine that could."
While Garner had no trouble fitting into her role as producer, she says her part as a single mom in the movie was "its own bear to get through."
"Anytime that you're playing someone who is going through something, you have to just figure it out, and you actually -- believe it or not -- don't use your own life as much as you might think," said the actress, who filed for divorce from husband Ben Affleck in April. "It really is its own bear to get through."
"You just get into that place. That's your job, and then you shake it off, because you have to go home and raise your kids," she explained. "It's just like any other time I do a scene with an emotional place."
Garner may have played down the effort she put into the film's heartbreaking scene where her character finds out her husband is cheating on her, but director Emmett Malloy told ET that she really "went for it."
"That scene in particular, I know that Jennifer said that she popped a blood vessel. So that kind of sums it up," he revealed. "She just joined the crew and was really with it, and didn't have a trailer and just sat there every day in that house and did scene after scene."
"They'll have to get to J.J. [Abrams] for that," Garner teased. "I'm getting ready to do an action film. It's called Peppermint, and it's a movie that I really love the story and the script and I'll start it next month."
The Tribes of Palos Verdes opens in select theaters and on VOD platforms nationwide on Dec. 1.