HAIDER ACKERMANN jacket, $1,445, and trousers, $1,415, net-a- porter.com; JENNIFER MEYER wave rings, $625 and $1,950, and circle ring, $500, 888-222-7639 Photography by Paul Wetherell

TO SEASONED TELEVISION FANS, the news that HBO and the BBC are at last joining forces to coproduce this month's must-watch miniseries—the lavish five-part costume drama Parade's End—will not come as a shock. After all, the two networks are responsible for some of the most groundbreaking and addictive television of the last decade—with BBC shows like Sherlock and Luther finding popular footing stateside just as HBO's Girls and Boardwalk Empire have earned praise in the UK. If a meeting of transatlantic minds (and demographics) felt inevitable, then surely no actor better embodies this new alliance—and each network's silver-screen-writ-small sensibility—better than Rebecca Hall, who possesses a rare combination of British theatrical bona fides and Hollywood glamour.

Over the past six years, the London-based actor has achieved fame in both American movies and in London's West End. Thirty-year-old Hall's sterling theater credits include starring roles in Shakespeare's The Winter's Tale and Chekhov's The Cherry Orchard—part of her boyfriend Sam Mendes's much-celebrated Bridge Project, a three-year cross-pollination between London's Old Vic and Neal Street theaters and the Brooklyn Academy of Music. (Her father, Peter Hall, founded the Royal Shakespeare Company and ran the National Theater; her mother is opera star Maria Ewing.) At the same time, Hall has played everything from a Boston bank manager and Ben Affleck's romantic interest in The Town to an uptight grad student in her Golden Globe–nominated turn in Woody Allen's Vicky Cristina Barcelona—an enviable Hollywood resumé by any measure.

Photos: Close-Up on Rebecca Hall

Click to view slideshow Photography by Paul Wetherell

In Parade's End, Hall portrays Sylvia Tietjens, the socially ascendant yet morally promiscuous and occasionally cruel wife of a Yorkshire-bred aristocrat—played by Sherlock's pale-faced mastermind, Benedict Cumberbatch—whose attachment to an antiquarian vision of English society on the eve of World War I keeps him dangerously rooted in the past. Hall found the character of Sylvia immensely appealing. "I don't think it's very often that you come across characters that are intensely unlikable, borderline sadistic, complicated and yet redeeming at the same time," she says. "She was fascinating to me and very out of my realm of experience. She's a force."

Cumberbatch might say the same of Hall. "I just think she's one of the greats," he says. "I talked to Meryl Streep about her recently on the set of August: Osage County and said, 'I've only seen one other actress [besides Streep] who has this complete command over her character on a film set, and that's Rebecca Hall.' " Parade's End was something of a reunion for Hall and Cumberbatch, who appeared together in 2006's Starter for 10, Hall's first film role as an adult.

Parade's End was adapted by Tom Stoppard—his first major television project in 30 years—and directed by Susanna White, who helmed both HBO's Generation Kill and the BBC's Bleak House. The opportunity to work with dialogue written by Stoppard, whom Hall calls the "greatest living dramatist in the English language," was a major draw for the actor, as was her appreciation for Ford Madox Ford, who wrote the novel on which the miniseries is based. "Ford Madox Ford was very witty and dry and the humor comes out of a quite dark place, while Tom has a very strong sense of humor that's more rooted in intellectual wordplay," she says. "Yet the crossover between them culminates in something magical." A friend of Hall's since she appeared in his 2009 adaptation of The Cherry Orchard, Stoppard was often on set to instruct the cast, which includes Rupert Everett in the role of Sylvia's brother-in-law and Miranda Richardson as the mother of her main romantic rival. "Tom thinks in a different direction," says Hall. "If we all think left to right, he thinks the other way."

Though she manages to avoid "the glitz and fame aspects" of a career in the public eye—a trick she learned from her parents—it's more than likely that Hall will have to recalibrate her relationship with celebrity in May, when she appears in Iron Man 3. In the third installment of the popular franchise, Hall plays Maya Hansen, a brainy scientist who develops a secret weapon for hero Tony Stark. The role was a departure for her. "The question became, Why not?" she says of taking on a summer blockbuster. "I kept not doing them and got to a point where I was like, actually, instead of deciding that it's not going to be for me, I should find out if I might enjoy it." As it happens, the experience felt much less foreign than Hall had anticipated. "One of the great things about the Iron Man franchise is that they employ fascinating actors who don't necessarily do action movies," she says. "Before Iron Man you didn't associate Robert Downey, Jr. and Gwyneth Paltrow with those kinds of films. There's an emphasis on repartee and wit."

Even with her induction into the ranks of superhero movies, Hall refuses to leave the footlights entirely. She set a rule for herself: For every three films, she must appear on stage at least once. "I'm not snobbish about it," she says. "I don't think that theater is the higher medium, that it's better than film." Whatever the setting or script, Hall's knack for choosing enduring roles comes down to a simple principle: "I'd rather that people say, 'Do you think you could do this?' And for my initial instinct to be, Oh god, no... how could I? And then to work it out. That's when it gets interesting."