“I think this Fall is going to be my moment to finally acquire a poodle,” says Greta Gerwig, sounding exactly like Greta Gerwig. She’s walking through New York and every bit of chit-chat could be a line from one of her charming, off-kilter films. She warns of “the risk of the walking interview” (police sirens). She talks of eating like a wolf. She enthuses about a 1926 novel called Lolly Willowes (“It’s kind of about a woman who becomes a witch!”), recommended to her by director Todd Solondz after she asked him for reading lists “because I wanted to know what was on his bookshelf”.

Eating like a wolf and requesting reading lists. These are related. On screen, Gerwig’s most enduring characters are both blessed and afflicted by puppy dog eagerness. Throughout her 10-year career she has acted with a mesmeric naturalism, exuding a palpable intimacy; you watch and feel as if you’re tumbling along with her. She may have been given frivolous labels like Indie Queen and The Meryl Streep of Mumblecore but they underestimate the connection she makes with audiences of all kinds. As much as any actor out there, Gerwig is a generational touchpoint. But at the same time, 70-year-old women will grab the 32-year-old in the street and tell her “I am Frances”, after her bumbling ballet dancer Frances Ha. She just connects.

Gerwig first made her name in no-budget indies such as 2008’s Nights And Weekends, a film that portrays a relationship about as honestly as it gets; sex and love all raw and clumsy. She went on to work with Woody Allen (To Rome With Love) and Whit Stillman (Damsels In Distress), but found her calling with Noah Baumbach, who directed her in Greenberg, Frances Ha and Mistress America (he is now also her partner). She co-wrote the final two films and her performances – physically hilarious as they are emotionally vulnerable – are the best showcases for her talents to date.

Gerwig lives in New York but is originally from Sacramento in California. She paints her younger self as a dorky go-getter, a Lisa Simpson type who played trumpet, excelled in fencing (ranking third in California) and ballet. At her all-girls Catholic high school she became a certified aerobics instructor and, at 16, a certified paralegal. She moved to New York in 2002 to study English and philosophy at Barnard, did lots of drama and theatre, graduated in 2006 and went into acting, immediately landing a role in LOL, a film by mumblecore auteur Joe Swanberg.

Gerwig in her breakthrough film Frances Ha. Photograph: Rex

In her latest, Rebecca Miller’s Maggie’s Plan, Gerwig plays a single woman with hopes of becoming a mother, who attempts to impregnate herself via a friendly sperm donor. Then she falls into a relationship with John, a married professor played by Ethan Hawke. Finally, she tries to fix the universe for everybody, conniving to make John fall back in love with his wife (Julianne Moore). It’s a screwball comedy with nuance – typical Gerwig in other words – but the character’s situation is markedly more adult territory.

“Every film I’ve done, I don’t think I could have done [earlier],” Gerwig explains. “I try to bring everything I’ve got to it in that moment. There are a lot of love stories in Maggie’s Plan, but the deepest, truly romantic one is between Maggie and her daughter. Even though I’m not a mother yet, I love having motherhood be part of the movie and I felt like I had a capacity for it I wouldn’t have had a few years ago.”

Gerwig has always invested much of herself into her characters, but has a particular kinship with those she wrote with Baumbach. Frances Ha’s breezy yet stifled dancer shares with Mistress America’s frothy socialite Brooke not only an unbridled energy but also the same ambition and self-absorption. I ask her how much they relate to her own personality. “Both of them align with my rhythms and my worldview in some way that I can’t even totally articulate,” she says. I wonder aloud what a psychiatrist would make of all this. “Well my psychiatrist has a very fun time with all of this! She’s more Freudian so she doesn’t really tell me [what she thinks], but she says it’s interesting that I recreate things but then I change them. I think I have to start with something that feels part of myself that I can spin out from that. It’s like telling a good lie. There’s got to be some truth in it.”

Looking inward to play these characters, she says, allows her to develop as a person. The 2012 romantic comedy Lola Versus made her feel comfortable with solitude. Maggie’s Plan has made her muse on motherhood. Actors often talk of how their own lives influence their work, but it sounds as if Gerwig takes as much from her characters as she gives to them. “I feel like when I play characters I create a space in myself that feels like the character, and that doesn’t go away. Somehow you carry that with you. You let it go but a little piece of it remains.” More grist for the psychiatrist.

Gerwig in Lola Versus. Photograph: Allstar/Fox Searchlight

She doesn’t like to examine all of this too much, she says, as it’s entirely instinctive. “I don’t know if I know any other way to live,” she says. “It’s got to be some primitive scratching on a cave wall. I was here, this is what I saw, this is what I looked at. I don’t know how people make meaning out of their life, but this is how I’ve managed to create meaning in mine. It’s a compulsion, in a way.”

Gerwig’s best characters all have problems with reality. They are not who they want to be, or who they think they are. Maggie thinks she’s got everything under control when, of course, she hasn’t. Frances is stuck in the past. Brooke thinks honesty’s the best policy, without ever pausing to consider the consequences. At heart, though, they are all pure of intention and that, says Gerwig, is crucial.

“I’ve had to play people who are stuck, who are misguided, who do the wrong thing for the right reason and the right thing for the wrong reason,” she says. “I’ve played people who are complicated, but I’ve never really had to deal with what I think the problem of evil is in the world. Not in a part, or in anything I’ve written. So I don’t know what that would be like. I have a fundamentally hopeful view about people, and that might merely be a reflection of the fact that I’ve lived an incredibly privileged life in a very wealthy nation without a lot of the struggles that most of the world has to face. So I can’t say absolutely that my lens is the correct lens. But that said, I love people and I believe in people’s essential goodness.”

Gerwig with Maya Rudolph in Maggie’s Plan. Photograph: Rex

With all of this input and output – those little pieces that remain – it sounds as if she’s becoming an amalgamation of her own characters. “Yeah! That’s how I experience it. I don’t know how you’d avoid having some of it rub off on you.” By not investing so much, probably. “Yeah. You could always not invest, but where’s the fun in that? It’s like when people say: ‘I don’t really care about holidays, or Christmas, it’s just a day.’ And I say: ‘Well yes, of course it’s just a day, but this is all we’ve got! We go around one time, let’s celebrate some stuff. Let’s invest!’ It’s not necessarily logical to do so, but what else are you gonna do with your life?”

And that, flying off in all directions, is the appetite for life that Gerwig shares with her on-screen characters and with which audiences identify so directly. Her characters are frank, funny, wide open and, at heart, good people. Whoever she plays, there’s an essence of Gerwig that breaks through, intentional or otherwise. We’re left feeling as if we’ve spent time with someone real.

Maggie’s Plan is out on Friday July 8