Zooey Deschanel has been melting hearts now for almost a decade, since her supporting role in Cameron Crowe's Almost Famous, her second film after debuting in quirky comedy Mumford with Hope Davis and Jason Lee in 1999.

Proving herself today as a worthy heart-breaker in her new movie (500) Days of Summer, she's excited to be twisting traditional male/female casting so that she's the one wearing the pants in the relationship. Joseph Gordon-Levitt's Tom is left licking his wounds after her character, Summer, dumps him.

The remarkable thing is that, according to US box-office statistics, male audiences actually seem to enjoy their long overdue comeuppance.

Download the new Independent Premium app Sharing the full story, not just the headlines

"We all know guys who've had their hearts broken in real life; we just don't usually see it in the movies," Deschanel agrees. "I know, like, 10 of these guys!"

Despite a string of high-profile roles in The Happening, Yes Man and The Hitchhiker's Guide to the Galaxy, Deschanel is still considered an indie girl, and this is the kind of delicious role that Hollywood usually reserves for its top-dollar leading ladies.

Still pinching herself that first-time director Marc Webb even cast her in Summer, which has since turned out to be one of the most critically praised movies of the year, she says: "I was so very flattered. To be honest, its not the way I think of myself. But if he'd picked one of those girls, you know, one of those beauty girls – those actresses of whom everything thinks, 'Oh my God, she's just so amazingly beautiful', and that's their thing – I don't think it would have worked. Because this is partially romanticising a little bit of quirkiness, which I feel is one of the interesting things about the movie. Summer is such a fascinating character because she's seen entirely from Tom's perspective as this ideal woman, when she's actually just a smart, interesting girl with her own set of problems. I've personally never wanted to be 'the babe', and refuse to let vanity get in the way of my acting because I don't see my job as being a beautiful person," she insists.

If we've all heard countless stories about actors actively soliciting roles, Deschanel laughs at the notion she might have gone after this part: "I never go after roles. Ever. It never, ever works for me. I was so excited when I read the script because it's so rare to see a romantic comedy that's really fresh and different. It felt like a new way of telling a story we think we've all seen before. But Marc had an idea of the film he wanted from the beginning, and I think I was part of that – he just had to go about convincing people to cast me, or let him cast me!" she laughs. "I've never pursued a role. I always hear stories about actors going after parts and I'm, like, 'How do they do that?' It seems so weird. It seems like a total myth or something.

"I've always been really picky about roles and make a point of reminding myself that it's not about the money – because, obviously, there's a lot of money to be made in this business if you're willing to do anything."

Talking about the role reversal in (500) Days of Summer, she says: "I don't think it has anything to do with gender specifically. I think it's more that, with our generation, those gender roles aren't something that really apply anymore. There are lots of guys who get heartbroken and lots of girls who are cynical about it. Another thing this movie says is that, just because love doesn't last, it doesn't mean it doesn't have value. You will discover things about yourself if you're being romantic even if it doesn't last. Love can mean a lot of different things.

"Fear of losing it is the dark side, but the wonderful side is the feeling that you get when you fall in love. Everyone has the heart-break that shapes them in such a way that they could never go back to the innocence that they had before. Today there's a lot of polarisation of points of view. People are either very cynical or overly romantic about love. Like somebody's in love one day, and then the next day, they're totally out of love – and I think that's sort of a new thing."

Despite the fact Deschanel, 29, has been engaged the past year to the indie rocker Ben Gibbard of Death Cab for Cutie, she's thoughtful when asked if she believes in love at first sight: "I believe everything is out there. Love is such a universally appealing theme. It just depends on your point of view. In some way, it exists in thought form. If it has a name, then you are creating it. I think people who try to force a relationship that's not happening are just insane."

However, she has clearly given some thought to what is romantic and what isn't – and Twitter, Facebook and internet dating definitely fall into the latter category: "They just don't seem romantic to me. I think there are great things about the internet, and there are great things about being able to connect with people quickly, but I also think it's strange to have your taste in music, and the movies and books you like be your calling card. I like this music, and I'm in this mood, and all that stuff, has nothing to do with who you are as a human being. It's just not so interesting to me."

The daughter of the Oscar-nominated cinematographer and director Caleb Deschanel and the actress Mary Jo Weir, she was named after Zooey Glass from J D Salinger's novella Franny and Zooey.

Together with her elder sister, Emily – presently starring in the television series Bones – they were educated at Santa Monica's artsy Crossroads School, whose alumni include Kate Hudson, Jake Gyllenhaal and Jack Black.

"Our parents gave us advice all the time which, of course, we ignored. Ultimately they encouraged my sister and I do to what we love to do and do what we want to do, so that started us off with a sense of 'Do this because you love it', not 'Do this because you want to be famous'."

Ever the rebel, she quit theatre studies at Chicago's Northwestern University after seven months: "I started working before I entered as a freshman, and it was difficult to deal with all the petty politics there. You had to be good at kissing up, which I'm really bad at," she admits.

(500) Days of Summer has received enormous critical praise in the US, but a USA Today critic Claudia Puig went one step further, claiming that it captures the same contemporary romantic sensibilities as Annie Hall did for a previous generation.

Delighted by such comparisons, Deschanel says: "In terms of style icons, I've always really liked Diane Keaton because she's totally herself and [in her] you see a person who isn't looking to anyone else. She's just saying 'I want to wear menswear,' or 'I want to wear this really long peasant skirt to the Oscars'. She's somebody who's just completely expressing herself. In the same way, I feel my choice of clothes helps project who I am on the inside, which I think is the best way to use them – to show how I'm feeling on any given day."

However, she's none too thrilled by those critics who liken her eclectic style – not to mention her signature black hair and bright blue eyes – to the pop starlet Katy Perry: "I don't really have an opinion on it, I guess. I think we both have ... hair," she frowns.

A singer and musician for as long as she's been acting, her dual careers often overlap. While crediting her singing skills as one of the main reasons she was cast as a department store singer opposite Will Ferrell in Elf, she also sang in the Disney TV movie, Once Upon a Mattress.

Tease her that singing is perhaps a contractual requirement, and she pouts: "I try to avoid it. I'm very sceptical of it because it has happened a lot of times like, 'Wouldn't it be cool if you could sing ...' They always feel they need to figure out an opportunity for me to sing. You really don't, unless it's a musical, because it gets complicated, as you have to sing in character, and somebody has something to say about how you sing. But, for Summer, all I had to do was karaoke," says the actress, who last year earned rave reviews for her debut album, She & Him: Volume 1, made in collaboration with M Ward, as well as appearing in videos for Jimmy Fallon's "Idiot Boyfriend" and The Offspring's "She's Got Issues".

While largely spurning what she describes as pop music, she jokes how her first album was Madonna's Like A Virgin: "It was during the time of the problems with Iran, and I thought she was saying, 'Like a Persian'!"

A fan of Ella Fitzgerald, the Beach Boys and Marianne Faithfull, Deschanel plays the piano, banjo, xylophone and baritone ukulele, and has been performing with the cabaret act, If All the Stars Were Pretty Babies, since 2001.

Previously dismissive of fellow actors launching musical careers on the back of their day jobs, she says: "For the longest time, I thought that any actor who released an album must be the biggest fool ever but, having been a singer all my life, I've now changed that opinion. No one gives musicians any flack for becoming actors, so I don't see any problem in it working in the opposite direction."

'(500) Days of Summer' opens on 2 September