Greta Gerwig is having coffee and a bowl of jasmine rice in a mostly empty SoHo restaurant on a frosty late afternoon in December. The day before, she was named best director by the National Board of Review, the first of many accolades that she, her star Saoirse Ronan and their movie “Lady Bird” will receive in the coming weeks. Gerwig is beaming, though you get the feeling that’s her natural state. Her short hair is blondish, with dark roots, and you can see an echo of a number of the characters she’s played — the ebullient falling-through-the-cracks dancer of “Frances Ha,” the Bowie-headed art punk of “20th Century Women” — in her large sun-dazed smile, her easy open laugh, her tossed-off intelligence.

“It wasn’t until I actually started writing ‘Lady Bird’ that I thought, ‘Where’s this movie? Why hasn’t this one been made?’” says Gerwig. “John Hughes movies I love; they loom so large for me. But that’s not what it felt like, did it? That’s not what it is inside. I wanted to show what it was inside.”

Julian Broad for Variety

Fusing their voices and talent, “Lady Bird” represents a seminal moment in the careers of Gerwig, the mumblecore actress-turned-indie It Girl-turned-screenwriter-turned-director, and Ronan, the 23-year-old Irish-American star whose performance has made her an Oscar front-runner for best actress.

This is the first movie Gerwig has written and directed, and just as she has emerged from the indie world, at 34, as a titanic filmmaking talent, Ronan, after a series of highly revered performances, raises her game to a new peak of emotional purity. There have, of course, been plenty of acerbic hipster high-school girls in movies, but none with this popping-off-the-screen intensity of searching, stubborn passion.

Ronan, as a stringy-red-haired parochial-school semi-misfit named Lady Bird (née Christine McPherson), occupies the furious center of a movie that looks outwardly small-scale. Yet “Lady Bird” possesses an uncanny quality, one that you saw in the New Hollywood films of the ’70s and the indie classics of the ’90s. It has a powerfully distinctive voice — bold, darting, sneaky and new.

Gerwig calls Lady Bird a character who makes no apologies. “She’s a young woman who’s able to stand inside her own desires,” she says. “She is lustful; she wants things. Not to get too gender studies about it, but she’s not waiting for anyone to look at her. She’s the person doing the looking.”

There’s a way to read the current moment that connects “Lady Bird” to a new world of opportunity for women filmmakers. Gerwig came of age admiring directors like Claire Denis, Agnès Varda (Gerwig on Varda: “You’re just as good as Truffaut, or Godard, or your husband!”) and Kathryn Bigelow (when she won the Oscar for director, it said to Gerwig, “This is a job available, to you”). And in a year ruled by the pop gender explosion of Patty Jenkins’ superheroine blockbuster “Wonder Woman,” and one that has ended with nothing less than a paradigm shift in the issue of sexual harassment, “there’s something coalescing,” says Gerwig. “Every year they come out with the numbers. You know, out of the top 100 films, by gross, 4% are directed by women. I think those numbers are going to shift. And it seems like it’s going to be less and less its own category. There are just going to be … directors.”

In the two months since “Lady Bird” was released by A24, the indie maverick behind 2016’s Oscar-winning “Moonlight,” Gerwig’s film has become the rare independent feature that’s a crossover hit ($30 million and counting), a critical darling (99% fresh rating on Rotten Tomatoes) and a major awards player. Showered with praise from critics groups, and with four Golden Globe and three SAG Award nominations, the film is now being talked about as a serious contender for best picture at the Academy Awards. Yet what all the success adds up to — and can’t entirely measure — is that “Lady Bird” has become a touchstone, a generational movie landmark hailed for its declaration of a bold new way of seeing.

“I’ve had girls, really smart girls, come up to me, and they’re so excited that they’ve finally got their movie,” says Ronan. “A lot of them say, ‘That was me! I was Lady Bird.’ The film has actually made them understand that whole period a bit more. You feel like it’s almost a photo album you’re looking back on.”

“There’s something about Saoirse on-screen,” says Gerwig (right) of Ronan. “You feel like you could look straight through her, like you can see her insides and her brain working.”

Courtesy of A24

Ronan creates a portrait of teenage experience that’s both irresistible and indelible, and Gerwig builds a world around her that is naturalistic yet invisibly heightened — as sharp-tongued as a screwball comedy but as spontaneously humane as a movie like “Boyhood,” presented with a bravura showmanship that whizzes by with a blink-and-you’ll-miss-it audacity.

“There’s something about Saoirse on-screen,” says Gerwig. “You feel like you could look straight through her, like you can see her insides and her brain working. I want an actress to feel like she’s in full possession of the character — not like you’re lending it to them, but that they own it.”

Ronan, sipping tea in the bar of the Four Seasons Hotel in Midtown Manhattan, wearing hoop earrings and a scarf over a crushed-velvet top, her hair pulled back, talks effusively about why she was so drawn to the character.

“What I knew would be so exciting about playing her,” she says, “and what was also really scary about playing her, is that she’s sort of trying on all these different roles, to see which one fits best. One minute she’s the showman onstage, and the next she’s the adoring girlfriend, and the next she’s the girl who’s going to pipe up in school,” explains the actress, still sleep-deprived from the night before, when she hosted “Saturday Night Live” and was up all hours at the cast party. “She’s testing them all out. She’s testing herself all the time.”

Ronan got oriented toward role-playing at an early age. She was born in the Bronx, but her parents came from Dublin and moved her family back to Ireland when she was three. She was homeschooled and learned a lot of what she knows about high-school society from watching teen comedies. If you look at the roles that have won Ronan the most acclaim, like the teen assassin of “Hanna” (2011) or the cross-cultural ’50s romantic of “Brooklyn” (2015), you’ll see a pattern that’s almost unconsciously etched: She plays young women who are lured out of their comfort zones, who push themselves from one space to the next.

“I admired how brave Lady Bird was to just take a risk and potentially fall flat on her face,” she says. “I think there’s something very admirable in someone who just goes, ‘F— it! I’m gonna do it anyway.’ And I love the complexity of her. You don’t get to see teenage girls like that on-screen. They’re always longing after a boy.”

Gerwig and Ronan worked closely together to create the character of Lady Bird, starting with her look. They collaborated on how to do the chopped dyed hair (the color choice was Gerwig’s, the cut Ronan’s), and Gerwig invited Ronan to rotate her own costumes (“She’d say, ‘Oh, I think Lady Bird would wear this today’”). Most strikingly, when a stressed-out work year — and too many hours under hot lights and makeup during her 2016 Broadway run in “The Crucible” — resulted in Ronan’s skin breaking out, Gerwig gently suggested that she not cover up her acne for the film. “I wasn’t insecure about it, for whatever reason,” recalls Ronan. “I just felt totally game to do it.” It turned out to be a unique touch, part of what makes Lady Bird such an authentic hell-bent girl with issues. The trust that grounded their collaboration took off from there.

“I think where Greta came from was both of us sort of wanting to be Lady Bird a little bit,” says Ronan. “We were both in a very open state. And this was a raw character. There was nothing to hide behind.”

“Lady Bird” is loosely based on Gerwig’s own life, but it’s far less autobiographical than many people still realize. Gerwig, like her heroine, grew up in Sacramento, was a musical theater bug and had a case of wrong-side-of-the-tracks real estate envy (“I think anyone who grows up in Sacramento, if you didn’t live in the Fabulous Forties you wished you did”). But she never made anyone call her by a different name, never dyed her hair bright red and never engaged in a senior-year battle with her mother over whether she could go to college back East.

“The goal is that everything in a movie has meaning. Nothing is just there because it’s there. We spent a ton of time layering Lady Bird’s room, talking about picking the paint color she would have chosen when she was a little girl. We wanted every image to have integrity, so that it didn’t feel adorned, but that it felt placed.”

Greta Gerwig

“So much of what Lady Bird is was this very flawed but fantasy heroine I created,” says Gerwig. “I was so rule-following and people-pleasing and gold-star-getting. I didn’t want to rock the boat. I was always me, but I wasn’t like how she is. Her kind of innate bravery. Just kind of the going-for-it quality — I didn’t have that. I was much more coloring inside the lines. But I think, for me, art was always the place where I could go too far.”

But what about Lady Bird’s thoughts — all those drop-dead one-liners? “No!” she says, laughing. “I think some of the things, but I would never say them.”

We used to call it “girl power,” and it’s true that movies, over the years, have given us a great many strong and liberated young women. Yet the revolutionary spark of “Lady Bird” is embodied not just in Ronan’s go-for-broke, inner-fury performance but in the film’s brilliantly executed structure and design. It’s a movie that walks a high wire. The scenes flash by as a series of moments — snapshots of life — held together only by the breathless bravura of Gerwig’s filmmaking.

The effect is to create a flow of coruscating emotion in which each moment becomes special — not because it’s servicing an “arc” but because it simply is. Near the end, when Lady Bird steps out of a church after a night of binge drinking, she has an epiphany: not just that her hometown of Sacramento is a lovely place, but that the life she’s been desperately longing for is the one that she’s been living. It’s the most moving — and spiritual — scene in any film this year, and it becomes a statement about the lives of young women. The film says: Every moment of your life is transcendent, as long as you’re alive to it.

Gerwig has always wanted to direct movies, going back to when she got her start in indie films like “Hannah Takes the Stairs” (2007), which were openly collective efforts. “When I was acting in those little movies,” she recalls, “I was also able to write while I was acting, because we had the characters and the plot devised, and we were speaking improvisationally. It felt like a way of sort of testing what worked as a writer.”

She didn’t dive headfirst into screenwriting until the two films that she co-wrote with her partner, the filmmaker Noah Baumbach. The first, “Frances Ha” (2012), is a remarkable little movie, and watching it you can see the formative stage of the Gerwig aesthetic: It, too, is a film that finds its truth in the flow of moments.

Gerwig constructs her scripts that way, but it’s more than a matter of stringing together anecdotes. “It almost feels like weaving,” she says. “I’ll put everything out in front of me when I’m writing, and I’ll almost arrange it like a quilt. And I feel like I’m pulling things through. As you move from moment to moment, it doesn’t feel like anything’s signposted for you, but a third of the way through you realize it’s starting to catch under you.”

Gerwig says she learned how to direct by soaking up everything she saw on the movie sets she worked on as an actress; she refers to that as her film school. She orchestrated “Lady Bird” with meticulous fervor, citing the Terrence Malick of “The Tree of Life” as an inspiration. “The goal,” she says, “is that everything in a movie has meaning. Nothing is just there because it’s there. We spent a ton of time layering Lady Bird’s room, talking about picking the paint color she would have chosen when she was a little girl. We wanted every image to have integrity, so that it didn’t feel adorned, but that it felt placed.” The result is a movie that looks — and feels — like life.

All of Gerwig’s collaborators speak with reverence of the precise but nurturing environment she established on the set. “She felt like our parent,” says Ronan. “Very protective over us.” Gerwig played a lot of music and threw dance parties as pick-me-ups, and her indulgences were limited to the occasional demand for what became known as “the Greta”: a Diet Coke and a bag of Cheetos. (Says Ronan, “I’ve never seen someone eat a bag of Cheetos so quickly in my life.”)

“She just doesn’t have fear,” says Scott Rudin, one of the film’s producers. “Most people have it, but I don’t think Greta does. She has a very natural confidence that comes from the knowledge that she’s the best person to be doing the thing she’s doing. She had people pulling for her, which is a very rare thing.”

Tracy Letts, who plays Lady Bird’s forlornly protective father, relates a telling story about how Gerwig allows herself to be guided by her instincts. The two first met at the Sundance premiere of “Wiener-Dog,” a movie both had acted in (in separate scenes). Letts says it was at the premiere party that Gerwig realized he was “an old softie” rather than the hard-ass she’d seen him play in movies and TV shows. She later offered him the role of Larry McPherson based on that meeting. “She really draws people to her,” says Letts. “People are magnetized by Greta’s energy, her personality. People want to be in the room where Greta is — literally.”

The daughter-mother relationship between Ronan’s Lady Bird and Laurie Metcalf’s Marion is multilayered, including Marion’s desire to keep her daughter from leaving home.

Courtesy of A24

“I’m spoiled rotten now,” says Laurie Metcalf, who has been vacuuming up awards — and who, at 62, has seen her career get a fuel injection — for her heartbreakingly funny, true-note performance as Marion McPherson, Lady Bird’s complexly adoring, controlling, embattled mother. “It was the most lovely set I’ve ever been on. It was stress-free, in that everything had been carved out, thought through, homework done. Greta has a strong maternal streak. She met with me and Saoirse a number of times to go through our scenes, and that allowed the actors to bring what they bring.”

The virtuoso skirmishes between Ronan and Metcalf turn “Lady Bird,” at times, into a rarefied cousin to films like “Terms of Endearment,” though in this case the mother-daughter conflict is spectacularly layered: It’s about money; it’s about jealousy; it’s about what education really means; it’s about Marion’s raging and desire for her daughter not to leave the nest.

At the same time, the film is a timely testament to the romantic power of female friendship. In the course of the movie, Lady Bird acquires two boyfriends, yet the movie is never a “love story,” unless you count the break-up-and-make-up trajectory of her relationship with her best friend, Julie (Beanie Feldstein), whom she thinks she’s outgrown.

“I watched the movie with my own best friend,” says Ronan, “and we’ve had so many romantic moments together where we just, like, declared for each other. And to see that on the screen, and to see her get out of the front seat and get rid of the boy, because that’s not what she needs — she needs to be there for her friend — to me, that’s the moment where Molly Ringwald goes out to the car, and he’s waiting for her.” It’s John Hughes, all right — or as Gerwig explained it to Ronan, “your boom-box-over-the-head moment.” Only this one shows what it is inside.

Letts, for one, thinks the sky is the limit for Gerwig. “I hope they give her a ‘Star Wars’ movie, if that’s what she wants,” he says.

Ultimately, what the triumph of“Lady Bird” means for Gerwig is the freedom to follow her bliss. She confesses that she was surprised at how much she fell in love with directing. “It’s simultaneously something that’s in your control and utterly not in your control,” she says. “And that paradox is very appealing to me. The illogical nature of making movies is appealing to me as well. It’s a reverse magic show. It’s so much time, and weight, and money, and people, and you’re taking all this stuff and you’re reducing it to flickering light, making it disappear into a dream. That feels satisfyingly strange.”