There aren’t many empathetic characters in “Black Mass,” the story of notorious Boston gangster James “Whitey” Bulger and his alliance with FBI agent John Connolly. The Scott Cooper-directed film stars Johnny Depp as a violent and calculating Bulger, alongside Joel Edgerton as Connolly, who’s portrayed as a man most loyal to criminals. Minor characters in the film are ruthless henchmen or somehow complicit.
The exception is Marianne Connolly, John Connolly's wife, played by Medford native Julianne Nicholson. She's the conscience of the film — the one who speaks for the audience and asks her husband why he would align himself with a guy like Bulger.
Nicholson, whose resume includes "August: Osage County," "Law & Order: Criminal Intent," and "Boardwalk Empire," understands the weight of her role. From the start, Cooper told Nicholson that Marianne Connolly was the moral compass of "Black Mass." She speaks up when her husband starts parading around in fancy mobster suits. She objects when he invites Bulger to her home for dinner.
"I'm watching and seeing in a real way what's going on," Nicholson said of her part in the movie. "Black Mass" was filmed around Boston last year, premiered at the Venice Film Festival on Friday, and has its US theatrical release Sept. 18.
Even though Nicholson, 44, is the only local lead in the film, she didn't pay much attention to the Bulger story when she was younger, partly because she was living in Western Mass. from the late '70s to the early '80s, the period of focus in "Black Mass."
Nicholson was back in Medford for sixth grade and went to Arlington Catholic High School. She wasn't in theater back then. She remembers that she did audition for a play at school, but she didn't get a role. "They offered me stage manager," she said, laughing.
From there it was on to Hunter College and modeling in New York, which led her to acting. Her first big roles were in two 1999 projects — Stephen King's miniseries "Storm of the Century," and "The Love Letter," which filmed on the North Shore and costarred Kate Capshaw and Ellen DeGeneres.
Since then, she's looked for roles onstage and onscreen that, like Marianne Connolly, have depth.
"If it feels like a fleshed-out person, especially for women," she said. "I want a whole woman there — I don't want to see an idea, or just one side."
Cooper said the casting of Nicholson as Marianne Connolly was key because of the character's place in the film. Not only is she one of the few women in the movie (Cooper confirmed this week that Bulger's girlfriend Catherine Greig, played by Sienna Miller, was cut from the story), she's arguably the most reasonable player in the narrative.
Nicholson's character is also an amalgam. FBI supervisor John Morris's wife, who is reported to have objected to having Bulger at her home (as Marianne does in a particularly dramatic scene in "Black Mass"), is also not in the picture.
"She is the only one who has the courage to say, 'enough is enough,' and leave," Cooper said of the Marianne character, adding, of Bulger's landscape, "It's an extremely male-dominated world."
Cooper said he'd long been a fan of Nicholson, but that he wanted her to portray Marianne because of her work in the off-Broadway play "Heartless," by Sam Shepard. "She was excellent. I thought she had a really natural style that was grounded."
He describes an effortlessness to her acting. "You don't see her work, which is what I like about her so much. It's exactly the kind of acting that I want."
Cooper said it's that quality that brings her to projects with formidable casts. In "August: Osage County," she shared the screen (and held her own) with Meryl Streep, Julia Roberts, Chris Cooper, Shepard, and Ewan McGregor. "Black Mass" has her in a cast that, in addition to Depp and Edgerton, includes Jesse Plemons as Kevin Weeks, Benedict Cumberbatch as Billy Bulger, and Peter Sarsgaard as Whitey's jai alai associate Brian Halloran.
Nicholson has ensemble scenes in the movie — inevitably, the Connollys and the Bulgers become uncomfortable dining companions — but she said her favorite moment to film was the dramatic scene with Depp, when Bulger finds Marianne in her bedroom and makes it clear that he requires her loyalty. It's an intimate, uncomfortable, breath-holding few minutes that has her quietly taking on a violent criminal. Nicholson said she and Depp filmed the scene in a few takes.
“We probably did it like three times. We didn’t do it a lot,” she said, adding, with a laugh, “I could have stayed there all day. Even with Johnny like that, I couldn’t see Johnny Depp anywhere under that character.”
Meredith Goldstein can be reached at Meredith.Goldstein@globe.com.