Photos of Gillian Anderson occupied a special place on Gabriela Hearst’s spring fashion mood board. “She was my muse,” Ms. Hearst said. “So sexy, so strong: the image of intelligent beauty.”

So when Ms. Anderson turned up in the flesh at the Hearsts’ West Village townhouse last week, wearing a breezy striped dress of Ms. Hearst’s design, the moment seemed surreal. Conversation, up to then a lively mash-up about breeding polo ponies and cloning men, came to a brief but pregnant halt, all eyes fixed on the actress, whose open-faced candor seemed at odds with her signature roles.

Ms. Anderson, 47, has after all honed her craft portraying weirdly troubled heroines: the special agent Dana Scully in “The X-Files,” Lily Bart in “The House of Mirth,” the police superintendent Stella Gibson in “The Fall,” and most recently Blanche DuBois in a revival of “A Streetcar Named Desire” first staged in London and set to open Sunday in Brooklyn at St. Ann’s Warehouse.

She slipped out of character at the Hearsts, where she encountered a cozy scene: Gabriela dandling her 10-month-old, Jack, while friends and family gathered around — among them the designer and actor Waris Ahluwalia, Lauren Hutton and Ms. Hearst’s husband, the film producer Austin Hearst.

“Ooh, can I take you home?” Ms. Anderson said, cooing as she leaned over Jack, who was gingerly toying with Ms. Hutton’s straw hat. “Oh, it’s fine, let him play,” Ms. Hutton said, murmuring to no one in particular, never mind any havoc that the baby might wreak.

Recovering their balance over cocktails and canapés, the guests besieged Ms. Anderson. “When is ‘The Fall 3’ coming out?” Ms. Hearst wanted to know. “We’re all obsessed.” When would previews of “Streetcar” begin? What makes Blanche such a coveted role?

“I don’t think I necessarily knew that it was coveted, but I’d wanted to play her for years,” Ms. Anderson said. “When I started working on the lines, I realized I already knew one of the monologues by heart.

“Blanche is one of the most complex characters I have ever played, so innocent, desperate, grief-filled, sad and funny, so many layers there all at once.”

With that, Ms. Hutton leaned forward. “My mother was Blanche,” she said a bit sourly. Minnie Hutton, an aristocratic Southern belle once characterized by her daughter as a lethal beauty, “was deeply, downwardly mobile,” Ms. Hutton lamented.

Ms. Anderson nodded in empathy. “Blanche lives in fantasy,” she said. “That’s the only way she can survive.”

An actress, she knows, has a similarly precarious shelf life. Ms. Anderson, who was brought up in the United States but spent much of her childhood in England, toggles nimbly between crisp Americanese and a plummy British accent.

“I consider myself American, but in America I was only one thing,” she said of her nine years investigating the paranormal in “The X-Files,” a role that she recently reprised.

By contrast, “In England I was embraced as a holistic actor,” she said, and was promptly offered classic Dickens parts, among them the society beauty Lady Dedlock in “Bleak House,” and the eerie Miss Havisham in “Great Expectations.”

If her perceived Englishness has given her an edge among New Yorkers (and a bump in ticket sales), Ms. Anderson claims not to have noticed. Her success, she said, has little to do with an accent.

But as guests were being rounded up across the hall for a dinner of risotto and lamb, Mr. Ahluwalia begged to differ. We’re a nation of Anglophiles, he noted, grinning broadly, adding that he’d recently come across a T-shirt stamped with the image of Queen Elizabeth, the Union Jack and beneath them the legend, “Make America Great … Britain again.”

Under the watchful gaze of a rotund Botero nude, Ms. Anderson dismissed that notion, accidents of birth and breeding eclipsed, in her view, by the more formidable challenge of getting down the part.

She thoroughly excavates each role, a task she describes as a “forensic investigation,” parsing the lines — every comma, dash and sentence break. “When you play the punctuation right, everybody finally gets it,” she said. “You go, ‘Ah. … ’”

A self-professed perfectionist, she confessed that she suffered occasional bouts of near-crippling stage fright: “I’ve had panic attacks right on stage.”

Still, she copes. “You just keep going no matter what,” Ms. Anderson said, “and somehow your mouth just keeps moving.”