Courtney Sullivan: My family, and other social animals

Courtney Sullivan's new bestseller about changing US mores was inspired by her own family history, she tells James Kidd

'Am I a close observer because I'm a writer, or am I writer because I'm a close observer?' (MICHAEL LIONSTAR)

Shortly after Courtney Sullivan published her debut novel, Commencement, in 2010, she embarked on a book tour of the US.

When she returned to her home-state of Massachusetts, the Sullivans were out in force at a celebratory dinner in her honour. "There were probably 25 people at this very long table," she remembers. "One of my uncles stood up and gave a lovely speech. He said: 'We all love you so much and are so proud of you. And we really need to say this now because we know that a year from now, none of us will be speaking to you anymore.'"

This avuncular threat was inspired by Sullivan's second novel, then a work in progress but now a New York Times bestseller entitled Maine. An engaging story of family dysfunction, it follows three generations of the Kellehers – Irish-American Catholics who bear at least a passing resemblance to Sullivan's own Irish-American clan.

Sullivan is quick to emphasise that her uncle was not in earnest, but I wonder whether she had any misgivings when writing a story that was potentially so close to home. "Of course!" she laughs loudly, and cites a favourite joke of her father's as evidence: "Irish old-timers forget everything but their grudges." In reality, a different form of Irish-American folk wisdom prevailed. "My mother always said, 'Write whatever you want. Don't censor yourself. Sometimes it's better to beg forgiveness than ask permission.'"

Before Maine's success enabled her to write full-time, she worked as a New York Times researcher. I meet her in a diner in her adopted home town; she arrives a few minutes late, but armed with a novel excuse. While waiting for a train from Brooklyn into Manhattan, she was stopped and questioned by a police officer who thought she was playing truant from high school. Although Sullivan turned 30 last year, it's easy to see how one could make the same mistake: her slight figure, youthful looks and understated dress all speak of someone far younger. In conversation, she is smart and fizzy, deconstructing the romantic comedy He's Just Not That Into You one moment, asking after Kate Middleton the next, before concluding with a discussion of feminism in contemporary America. Throughout, she seems enthused with fresh wonder that she is able to write fiction for a living.

Maine represents a considerable advance on Commencement, a story of four graduates facing life after college. Largely set in the Kellehers' holiday beach house, Maine juxtaposes the promise of leisure with simmering family resentments. Sullivan suggests the premise had some basis in her own life. "When I was growing up, several generations of my family went away for a couple of weeks in a big house. When you slow down everything else in life, the tension has a way of exploding."

Sullivan's study of inter-generational conflict is partly a personal project. "I guess my writing tries to answer questions in my own life," she says at one point. But Maine also seeks to address broader questions raised by the past 60 years of American social history. There is Alice, the recently widowed Kelleher matriarch who sacrificed her artistic ambitions to raise a family, and tries to relieve present loneliness with alcohol and her Catholic faith. The youngest Kelleher is Maggie, Sullivan's alter ego, who is free to pursue her literary and personal ambitions.

"I was interested in how women in America are defined by the historical moment of their birth. Timing is everything. Maggie represents what Alice could have been had she been born 40 years later." At the same time, Sullivan argues, Maggie's relative personal freedom breeds new problems. "Having all the choices in the world does not necessarily make for a blissful existence. Sometimes it makes for a more complicated one."

Maine has been a critical and commercial hit in the US. Time recently named it one of its 10 books of the year. Some reviewers, however, dismissed it as "chick lit", a label Sullivan unpicks with a combination of acceptance and weariness. "It's frustrating, but also part of the territory of being a woman writing right now. Jane Austen is still considered a 'women's writer' while Thackeray is for everyone, even though he also writes about romance and social graces. No man is ashamed to say he's a fan of Annie Hall, but would any man name When Harry Met Sally his favourite film?"

Sullivan is living her own private romantic comedy right now: in the week between arranging the interview and our meeting in New York, she became engaged. While clearly happy, she is keen to avoid the excesses of the modern wedding. "Some of my friends who used to say how creepy they found the whole wedding culture reversed that opinion the moment they got engaged. It is like a Dawn of the Dead takeover."

By curious coincidence, the novel Sullivan is currently working on explores how marriage has changed in America over the past 100 years, through the prism of the diamond industry. "It's partly about how advertisers created the belief that diamonds are forever. But I'm particularly fascinated that our generation was exposed to the notion that marriage often doesn't work – either your parents were divorced or your best friend's parents were divorced – and yet so many of us are eager to just jump right into it. It's like a next generation do-over."

It is, Sullivan says, a second instance of life imitating art: one of Maine's sub-plots, about Maggie's relationship with her boyfriend, anticipated Sullivan meeting her fiancé. "Am I a close observer of things because I'm a writer, or am I writer because I'm a close observer of things?" she wonders aloud.

Whatever the truth, Sullivan's fiancé would do well to pay attention to the subject of her future works.

Maine, By Courtney Sullivan (Grove Atlantic, £12.99)

'... Kathleen imagined the three of them – Maggie, Alice, and herself – side by side, three generations of women absorbing power and wisdom from one another. She realized it was a mistake from the moment they arrived. The swami asked to inspect their belongings. Kathleen had expressly told her mother there was no caffeine or alcohol allowed, and Alice said that was fine by her. But when he unzipped her suitcase, he found two Ziplocs full of tea bags, three bottles of red wine, a large bottle of rum and a blender. A blender!'