Several years ago, when film-maker Mira Nair headed to India to shoot the final scenes of William Makepeace Thackeray's Vanity Fair (2004, starring Reese Witherspoon), she wasn't looking for inspiration for her next project. She already had two meaty ones well underway - screen adaptations of Tony Kushner's play Homebody/Kabul and Hari Kunzru's novel The Impressionist. Nair only wanted a novel to fill the long hours of the flight and so she picked up a book she'd bought six months before but hadn't cracked. What happened next was one of those rare magical intersections between art and life where the two seem to inform each other so profoundly that they are no longer separate.

The book was Jhumpa Lahiri's novel, The Namesake, and Nair's screen adaptation of it is to be released this month. Nair recalls the book touched her so immediately and profoundly that when she landed in India she called to see if the rights were available. A week later the film was hers. The timing was such that Nair read it when "I had just lost my mother-in-law and was in mourning," she says. What she found was an immense solace. "It was like some sort of balm to be understood in my loss and also to be perceived in the see-saw of my worlds," she says referring to the migrating back and forth between India and the US that has marked her own life since she left India at 17 to study at Harvard.

Nair's adaptation of the novel is nothing less than faithful to Lahiri's story, and yet the film is inflected, if not imbued, with Nair's vision of the world as she takes on with great pathos and deft comic timing such resonant themes as parent-child relationships, the nature of "what is home" and how marriages work-or don't work for that matter. For viewers who have not had to split their lives between two continents, Nair is able to convey-in a shorthand akin to poetry-both the richness and the sadness that is inherent to this existence as the film moves back and forth between Kolkata and New York City.

Late one afternoon, I catch up with Nair at her office off Union Square in Lower Manhattan, a high-ceilinged loft space with blond wood floors and tall windows, decorated with posters of vintage Indian cinema and of her own films. Two assistants are at work when I come in and I am soon ushered into Nair's private office, which aside from the desk, has low, comfortable couches and colourful pillows giving it a warm, calm and vibrant feeling not unlike Nair herself. She greets me with a hug though we've only met once before. Outside, the pale, wintry sky over the landscape of rooftops makes the office seem all the more cosy as we talk over chai and dates that the actor Kal Penn has brought back from fans of hers in Saudi Arabia - though I suspect Nair could make the inside of a military cargo plane seem cosy! She exudes an unusual combination of easygoing warmth and focus that makes the rest of the world seem to fade temporarily, whether she is talking about film-making, family or creating gardens.

In putting together The Namesake, Nair says she thought of it as "a kind of flag to desi power". In addition to hers and Lahiri's contributions, there was her long time writing partner, Sooni Taraporevala, a cutting edge British-Asian musician named Nitin Sawney who did the music and all the actors and actresses. "We were everyone from everywhere, but we were all from one subcontinent," she says. One of her central challenges was handling the 30-year span of the story "and not lose gargantuan steps." The answer, Nair realised, lay in looking at the two cities, Kolkata and New York (which Nair used instead of Lahiri's Boston), and trying to visualise them as one.

This unifying of two seemingly distinct locales, she explains, "is the state of mind and state of heart of a person like me who lives between places. You look outside at the Hudson River and it could be the Ganges one day". Also, she adds, "There is a similar energy. Both cities are slaves of excellence." In terms of motifs, she finds "the bridges of both cities are extraordinarily and iconically similar", and once she realised she could use both bridges and trees to bring the cities together for the viewer, things began to move forward from there.

One thing that strikes me about The Namesake is the way Nair is not afraid to take her time with certain moments, to let the camera simply watch, whether it is the scene where the family scatters the father's ashes in the Ganges, with the famous Baul singers of Bengal incanting their haunting songs, or images of the mother going about her work at the library or in the house. While there are moments of great swirls of activity, particularly as they relate to the children's lives, they are contrasted with moments of great stillness. This is no accident, Nair says. "The stillness is exactly what I wanted to achieve, because of the stillness of our parents' generation. When Ashok and Ashima (the father and mother) have a cup of tea, they only have a cup of tea. They do not need to be doing anything else. They don't even need to be looking into each other's eyes and saying I love you, but they do. I wanted the contrast between the stillness and courtliness of that life and the lack of it in young people's lives today."

The way she uses framing and music to convey this, she says, is very much inspired by the great Bengali film-maker Ritwik Ghatak's Meghe Dhaka Tara (or The Cloud-Capped Star), a film she admires for "the emotional intensity and the musicality" and the fact that it is "deeply personal and almost Soviet in its frames." The Namesake is dedicated to Ghatak and also to Satyajit Ray, who was Nair's mentor and introduced her debut film Salaam Bombay! to India in 1988, when his words appeared on the poster for the film saying, 'I cannot recall ever being impressed so much by a first feature. It is completely unlike any other film ever made in India and shows complete command over every aspect of the medium.' The vivid, sad, and painfully realistic Salaam Bombay! (1988) told the story of street children in Bombay (as it was called then) using mostly non-professional actors that Nair and her crew discovered in their travels through the city. The film quickly captured the world's attention, winning the Camera d'Or and the Prix du Publique at the Cannes Film Festival and then being nominated for an Academy Award for Best Foreign Film."

I tell Nair that one thing I was personally surprised by was how much The Namesake made me cry and I ask if she has encountered this reaction before. Nair, who at the time we meet has seen it with six audiences around the world, each about 1500 people, says she has been surprised by people's reactions. "People belly laugh, they cry and then they outright, audibly sob. They again come back to laughter, which is a wonderful thing." She has also heard from people of all different backgrounds, "whether they're Jewish, Icelandic, or Hungarian," that she is telling their story and she believes this is because the film is about loss.

Two of the most remarkable performances are by Irrfan Khan and Tabu, who play the parents, Ashok and Ashima. Nair knew from the beginning she wanted to work with Khan, but envisioned a Bengali actress for Ashima, though she had been wanting to work with Tabu for some time. The actress Nair ended up choosing then had scheduling conflicts and so Nair called Tabu, someone she describes as "an amazing actress from within," to see if she would be able to clear her schedule and do the movie for a role in which she would have to age 30 years.

Of her snap decision to make The Namesake, she says simply, "I feel grateful that one can have force of inspiration like that." As she describes the course of her career, it becomes clear that one of her central beliefs is that when it comes to one's work, "it's important to do something fully without thinking of reward. If you think of every thing as a stepping stone to something else you will never be ripe for the plucking. That is the key to what I do." It was this kind of openness that allowed her to do The Namesake and in a different way led her to make Monsoon Wedding (2001).

Some seven or eight years back, Nair was at what she describes a low point, having fought a six-month legal battle against the Indian government's ban of her film Kama Sutra: A Tale of Love (1996), and having just given up on a project she'd worked on for a year and a half. Then one day, she saw two women crossing the road in Mumbai "laughing like banshees" and she followed them and found out about laughing clubs. Uncertain of when she'd be inspired next to make a feature, Nair thought that she would make a short documentary, in the monsoon, which she'd always wanted to do. When she made The Laughing Club of India (1999) on the fly in six weeks, she thought she was making "an absurdist film as an antidote to my own despondence". So she was surprised to find the result was not only "oddly moving," but that it ended up being "directly the genesis, stylistically and emotionally, in every way, of Monsoon Wedding, which became the biggest hit I had made. If you look at those movies, it's the same style - a hand-held camera in the rain, old vintage love songs, the portrait of a city, people talking." And yet, she says with a kind of disbelief, "The Laughing Club was made for no reason, just for sanity and to feel alive."

This faith in the natural course of inspiration is something she tries to impart to her graduate students at Columbia University's programme in film studies. "I think if you give yourself fully to whatever there is, there are connections that are being made without your knowing it at first. Whereas if you force it, you lose that spark that makes you see something and drop everything."

By nature, Nair is a nurturer. In addition to her film-making, she is a passionate gardener and has created a number of lush, fruit-filled gardens, both public and private in Kampala, Uganda, which is home for her along with Delhi, though she spends time in New York City as well, where her 14-year-old son, Zohran, attends high school. (Her husband, the academic Mahmood Mamdani, is from Uganda, and Zohran, who shares his mother's lively sense of humor, calls himself 'Ugindian'.)

Nair has also started a film school in Uganda, called Maisha, for East African and South Asian students. Now in its third year, it runs year-round, and Nair has invited, to great response, film-making colleagues from around the world to come and teach two-week courses. "I'd done so much of this mentoring at Sundance and other places, and I thought, why not teach right there? (In Kampala), there is such dignity and power and poetry around me, and political engagement in every moment of my life, not to mention unmanicured beauty…(and yet) there's such a miss between what is and what is sucked out of somebody's thumb in Hollywood. I felt like we had to tell our own stories, or no one else will. It's about bringing the kind of education we have available to us here, that kind of high-level expertise and a fantastic audio-visual library, to young people there." It's clear in talking to Nair that she does what she does, because she feels compelled to. She says, "I don't like to say nonprofit, because it smacks of charity and that's not the point but I just have always wanted to do that."

Next, Nair says she is producing a series of four 12-minute Panavision films with three other Indian directors, to raise awareness in India on HIV and AIDS. "It's kind of a Decalogue-inspired thing that just happens to be 'Wake Up to AIDS,'" she says, explaining that at the end of 2007, when the masses go to see Bollywood movies, "they will first see a highly untraditional 12-minute film with the same stars, about AIDS". Her own short work, based on a true story, is "about the virus being the great class leveller of society". In it a migrant labourer in Mumbai who is graniting a building has a one-shot encounter with a neglected upper-class housewife whose husband secretly prefers men. The labourer goes back to the village, impregnates the wife he loves, and the baby is born with HIV. When I wonder at the fact that Nair will convey all this in 12 minutes, she only laughs and says, "Yeah, well, I make these movies."

She also admits she's superstitious to talk about it, but that she's on the brink of signing a massive film with a big movie star that will go between three continents. Only a few weeks later, it is announced that she will be directing Shantaram, starring Johnny Depp, based on the novelised account by Gregory David Roberts of his life as an escaped convict/heroin addict from Australia who reinvents himself as a doctor in Mumbai's slums and gets involved in the city's underworld.

When I read this in the local papers (I happen to be in Mumbai myself for a friend's wedding), I think how much Nair's own philosophy of dedicating oneself fully to the work and the inspiration at hand has proved to be a fruitful path for her. Whether she is engaged in making a feature (of which there are nine), a documentary (she's made five), or a short film (the HIV piece will be her third), she seems to move as effortlessly between genres as she does between cinematic milieus, be they a 16th century Indian court in Kama Sutra, working-class New Jersey in Hysterical Blindness (2002) or 19th century England in Vanity Fair. While at first glance Nair's films may seem disparate in their themes, when watched together there is an unmistakable boldness that unites them. Visually, it comes through in a lush, fill-the-frame style, but even more striking is the emotional aspect, an openness comprised of joy, audacity, and to-the-bone sadness. Nair herself describes it as "the unabashed quality we have not only in Indian cinema, but in Indian life of wearing your heart out there-which I don't confuse with sentiment, because I feel I am fairly ruthlessly unsentimental."