Jessica Chastain plays a Washington lobbyist in “Miss Sloan.” (Kerry Hayes/EuropaCorp Films/France 2 Cinema)

You can’t help but notice something when you stand next to Jessica Chastain: She’s kind of short.

The two-time Oscar nominee and 2017 Golden Globe nominee, who has made a name for herself playing strong characters such as the CIA analyst tracking Osama bin Laden in “Zero Dark Thirty” and the mutinous commander of a space mission in “The Martian,” is, at 5-foot-4, considerably less imposing in person than she often appears on the screen.

Meeting at a Washington hotel this fall to talk about her new film, “Miss Sloane,” in which she stars as an uncompromising yet morally compromised D.C. lobbyist, the 39-year-old actress laughs at the observation, saying only, in understatement, “Most of my characters are very different from me.”

In preparation for playing Elizabeth Sloane, an influence peddler who jumps ship from her high-powered agency when it takes on a pro-gun client and goes to work for a rival firm on the gun-control side, Chastain shadowed and interviewed 11 female lobbyists. Among her discoveries: The power suits and heels are a “battle uniform.” Pill-popping, which her character indulges in, is not unheard of. And black nail polish — as seven of the 11 women wore — is a thing. “What does that say about you?” Chastain wonders aloud. “That you’re polished, badass, hard and strong, powerful — and maybe not traditionally feminine.”

Many of Chastain’s roles offer a mix of the tough and the tender, or what “Miss Sloane” director John Madden, in a separate interview, calls “the formidable and the flawed.” It’s why the British filmmaker (“Shakespeare in Love”) says he cast Chastain, when she was not yet a household name, in 2010’s “The Debt” as a young Mossad agent. After that, Madden and Chastain were looking for a chance to collaborate again.

“Miss Sloane,” with a hero who has chinks in her suit of armor, was seen as the perfect vehicle. “I needed someone who can command the verbal dexterity, the speed, the ferocity of this character,” Madden says, “at the same time as offering the kind of fragility that Jessica always has about her.”

Actress Jessica Chastain and director John Madden take questions at a screening of “Miss Sloane” in New York on Dec. 4. (Robin Marchant/Getty Images for Academy of Motion Picture Arts and Sciences)

Chastain’s meticulous advance work on the role, during which she says she inadvertently overheard improprieties such as an offer of free travel from a lobbyist to a Senate staffer, was matched by Madden’s own fidelity to verisimilitude. The Glover Park Group, a D.C. communications and government relations firm, served as consultants, at one point entailing last-minute changes to the screenplay.

“We had a piece of wrong information in the script,” Madden says, “about whether the congressional gift ban applied to sovereign states,” a critical plot point. “It was very important that the underpinnings be as real and correct as they could be. That little discovery necessitated some intense and productive script surgery.”

The character of Elizabeth was loosely inspired by Jack Abramoff, according to Madden. Although Chastain read the disgraced lobbyist’s memoir, “Capitol Punishment,” she says she was more influenced by the determination of her agent, Hylda Queally, whom Chastain has watched fight for her.

“I do a lot of research before I get to set,” the actress says, “before I ever say a word. I’m very intuitive, but I also create a lot of back story. I look at a script like a detective.

“Sloane says to Jake Lacy [who plays a male escort used by Chastain’s character]: ‘I grew up lying. I didn’t want to. I had to. That’s why I excel at it.’ I thought about the pills. Why is she taking on the unwinnable case? Is it career sabotage? All that led me to a tale about addiction, inside the realm of the political process and the gun debate. The subplot of ‘Miss Sloane’ is that of a character who is addicted to winning.”

When it comes to discussing where they stand in the gun debate, both Madden and Chastain, who has never shied away from speaking out on progressive concerns such as sexism and ageism in Hollywood, deflected the question, arguing that “Miss Sloane” is meant to be provocative entertainment, not a polemic.

“It’s not my place to stand there and be saying, as an outsider, that this is what you people here in the States should be doing,” Madden says.

At the same time, he notes, he is not trying to equivocate either: “The film’s job is not to be fair to both sides of a political argument. It’s to be fair to both sides of a dramatic argument.”

For her part, Chastain — whose character is a Republican, by the way — says the film’s subject has less to do with the merits of either side’s argument than with the fact that guns are a convenient way into far more troubling questions.

“I do a lot of research before I get to set. . . . I look at a script like a detective,” Chastain says. (Kerry Hayes/EuropaCorp/France 2 Cinema)

“Miss Sloane” could never have been made about the “Nutella tax,” Chastain jokes, citing the term the film uses for the wonky debate on palm-oil imports that opens the movie. “Where someone stands on the gun debate isn’t even the question people should be asking about this film,” she continues. “It could be climate change, immigration, abortion. But something is broken in D.C. I didn’t know that senators and congressman will sometimes go to three fundraisers every single day — breakfast, lunch and cocktails or dinner — just to make enough money to keep their seat in office.”

In that regard, Chastain seems to be angling for an A-plus on the homework she has done on the way Washington works (or doesn’t). “I hope the film will open a discussion,” she says, “because from the outside, it feels like money is pouring in here, yet nothing gets done.”

“Miss Sloane” isn’t a documentary, Chastain says, adding that she nevertheless hopes it’s real enough so that people inside and outside the Beltway will recognize the city it’s set in. “I want to be in a film where people who work on and off Capitol Hill will see it and say, ‘Okay, that’s not just all complete fiction.’­ ”

Miss Sloane (R, 129 minutes). At area theaters.