On a recent Thursday afternoon, the actress Keri Russell paused in a corner of Brooklyn Bridge Park to admire a starling.

It was technically spring, though the weather had other ideas, and Russell, in subdued plumage, braved the wind in chunky boots and a black puffer jacket. Her hair was tousled. Liner ringed each eye, possibly a souvenir from the previous night’s too many margaritas with friends. She didn’t look much like a woman who devoted years of her life to undermining the American democratic project. Or like a woman now charged with safeguarding it.

But Russell has been both of those women (and a lot of other women besides). At this point in her career, she is probably best known for her six seasons on the FX drama “The Americans” as Elizabeth Jennings, a Soviet sleeper agent with an ambitious collection of ruses and wigs who earned Russell three Emmy nominations. Now Russell has taken on an opposing role: In the “The Diplomat,” a Netflix series debuting on Thursday, she stars as Kate Wyler, a savvy U.S. civil servant tasked with upholding America’s reputation abroad.

A veteran ambassador, Kate is about to take a post in Kabul when an international incident shunts her and her husband, Hal (Rufus Sewell), to London. An English manor house is not a war zone, but Kate behaves otherwise. Armored in punishing heels and sleek sheath dresses, she treats even polite conversation as battlefield maneuvers. But in a departure from “The Americans,” Kate’s work is almost entirely aboveboard. She wears no wigs.

As some Canada geese waddled nearby, Russell considered the disparities between these two roles. “It was fun being a baddie, doing sneaky stuff,” she said. But “The Diplomat” also has its pleasures, she insisted. “It’s awesome to be smart and capable and dress people down and be so steady about it,” she said.

If Elizabeth is a baddie, does that make Kate a goody? Russell gave a cagey smile. “We’ll see,” she said.

Russell began her career as a teenage dancer in “The Mickey Mouse Club” and then starred in “Felicity” as a capricious college student and the patron saint of dithery girls everywhere. She did not necessarily expect to spend her midcareer playing hypercompetent women while also showing the uncertainty that undergirds that competence. In addition to playing Elizabeth and Kate, she has also recently appeared as an indomitable mother in the horror comedy “Cocaine Bear” and as a cool, if not especially effective, assassin in “Extrapolations.”

Felicity would not have excelled at either espionage or high-stakes diplomacy. “Felicity would write a poem about it,” Russell said. But that was 20 years ago. Russell, who in person is outspoken, unfussy, charmingly profane and so candid that she encourages similar candor in others and now absolutely has kompromat on me, has grown up. She has since become a mother. She has two children with her former husband, Shane Deary, and a young son with her partner Matthew Rhys, her co-star on “The Americans.”

“Moms are like that!” she said of these recent capable characters. “You’re going to make it happen. A mom can do 37 things in one day!”

Russell comes to this park, near the home that she shares with Rhys and her children, on the rare occasions when she has an early morning to herself. Sometimes, before anyone else is awake, she’ll ride her bike through the park’s loops. “It’s a beautiful, happening place,” she said, pointing out the roller rink, the basketball courts, a meadow, the indelible view of Manhattan across the East River.

Over the last year or so, those mornings have been rarer. It was during the Christmas holiday of 2021, when Russell had volunteered to cook dinner for the children’s three sets of grandparents, that she received the scripts for “The Diplomat.” With Rhys already away for part of the year filming the gloomy HBO revival of “Perry Mason”—“I was already punishing him with guilt for not being home,” she said — she wasn’t looking for another starring role.

Still, something in Kate’s ambition and savvy, as well as the humor of her marital tussles with Hal, called to her. She agreed to a video call with the show’s creator, Debora Cahn, a veteran of “Homeland” and “The West Wing.”

Cahn had wanted Russell for the role, trusting that Kate would benefit from Russell’s beauty, grace and ability to convey emotions even in characters who control and repress their feelings. But Kate was a more neurotic proposition than past Russell characters — gorgeous enough to be the subject of a Vogue spread in the show but also sweaty, squirrelly, with a lot of angst behind the poise.

“There’s a part of Kate that is itchy and twitchy and always uncomfortable in her own skin,” Cahn said in a recent phone interview.

Russell was a woman of far more poise, Cahn assumed, but she knew that Russell was also a skilled actor. She could perform that discomfort. And yet, as she watched Russell squirm through the video call, she discovered that discomfort was part of the Russell package, too.

“I get really nervous,” Russell confirmed in the park. “I do really sweat a lot.” (She didn’t seem to be sweating here, though it was quite cold.)

This contradiction — glamour in the front, social anxiety in the back — helped Cahn explore the thesis of “The Diplomat,” which is that everybody sweats, even (or especially) the bodies in power.

“In Buckingham Palace, in the Great Hall of the People, everybody in there is still a leaky human,” Cahn said.

Kate, on the show, puts it more tartly. “You show people the nice parts because, believe me, that’s all that anyone wants to see,” she says.

The effort that Kate makes to maintain a flawless veneer resonated with Russell, though largely because she has never had much patience with or talent for the public-facing aspects of her profession — the interviews, the award shows, the times when she has to perform a more idealized version of herself. She used to beat herself up for this unease, but she has since accepted it.

“I’m like, that’s who I am,” she said.

And yet, sets are places where she has always felt at home. “The Diplomat” filmed last summer, mostly in London and mostly on location. Sewell had never met Russell, his work wife, until they were both in the hair and makeup trailer, but he was struck by her openness and ease.

“She immediately was very friendly and personable and easy,” he said. “I automatically thought it was going to be relatively straightforward working with her, because she was a lot of fun.”

Fun is not necessarily a word that anyone would apply to Kate or that Kate would apply to herself. However sweaty Russell feels herself to be, she moves through the world, or at least through the park, with less strain and tension. (And she is fun. At one point, she pulled out her phone and showed a picture of herself looking unhinged in an ash-blond wig, an outtake from “The Americans.” She sends the picture to her friends when it’s time to party. “We don’t let her have chardonnay anymore,” she said of the image.)

While Kate is a creature of ambition, Russell has always held her work more lightly, even as she pushes herself to give vivid, committed performances.

“When I’m there, I work hard,” she said. “I want to be good.” But she drew a distinction between herself and Rhys, even though they take on many of the same projects. (He is in “Extrapolations” and “Cocaine Bear,” too.)

“He likes to be busy,” she said. “I like to never be busy. I like to like drift away and roam the park.”

She was near the river now. The sun turned the gray water gold. Ducks dabbled. Unlike Kate, no one needed her to save the world today or to sweat through her clothes while neutralizing some new crisis. Hypercompetence could wait. She needed only to find her way back through the park and text Rhys to see if he could meet her at an Italian restaurant close by. Among the 37 things, there was just time for a beer before school pickup.