'She's the only writer for whom we've ever concluded a deal in Montenegro': Liane Moriarty. Credit:Nic Walker This seems quite a good illustration of Liane Moriarty's attitude to life, and one reason, perhaps, so few of us know who she is: she keeps her head while all around are losing theirs. But it also means that talking to her is not really the best way to get a sense of how unusual her path has been. If you want to understand how lightning-strike extraordinary it is to sell six million books, or how vanishingly small the chances are of an author earning in excess of $10 million from her books alone, as my calculations suggest Moriarty has, don't ask Moriarty herself, because she's way too modest to tell you. The jubilant amazement of her own publishers is a better place to start. "At one point last year she had three books on The New York Times best-seller list. Three!" exclaims her American publisher, Amy Einhorn, from New York. "Two were hardcovers, and those weren't even part of a series! That's unheard of." No other Australian has ever achieved this; nor has anyone from this country ever debuted at number one on the famous list, as Moriarty did with Big Little Lies. "Last year she was the top-selling Australian fiction author in this country, despite the fact that she had no new book out in 2015," says her Australian publisher, Cate Paterson. Her new book, Truly Madly Guilty, is expected to "break the internet" (as fan Annabel Crabb puts it) when it goes on sale this month. "She's the only writer for whom we've ever concluded a deal in Montenegro," says her agent, Fiona Inglis of Curtis Brown, sounding bemused. "She's sold into more territories than any other client in 49 years of Curtis Brown Australia. It's hard to imagine that discussions between parents in a Sydney beachside primary-school playground could translate successfully into Hungarian, Thai, Brazilian or Swedish, but it seems that in Liane's hands they do."

Styling by Matthew Stegh; Hair & Make-up by Wayne Chick. Credit:Nic Walker So why is she so little known here? Moriarty's Australian obscurity has been very real: a little over a year ago, Cate Paterson labelled it as her own "career despair" that Moriarty "hasn't exploded here like she has in America". And though Paterson has since slightly revised this judgment, she still wonders why it's been such a slow burn. "I've had a couple of festival directors saying: 'Oh, I saw her on The New York Times list and then found out she was Australian!' " she laughs. "And so suddenly, now [she's famous in America] she's being asked to every festival in town.' " Perhaps the most important thing to say about Liane Moriarty's obscurity is that it's selective. The book-buying public, clearly, knows exactly who she is: she's regularly listed at the top of reader reviews and ratings lists online, and she has an enormous, loyal coterie of fans all over the world who devour her books. But it's also true to say that, despite her incredible success, Moriarty has been the subject of a number of systemic problems within the publishing industry. And most of these problems are, depressingly, simply the result of being a woman.

There are always the most incredible lives going on behind the scenes. Liane Moriarty Publishing, despite its reputation as a civilised meritocracy, is a hard industry for women. It's been shown repeatedly that female authors are less likely to receive agent interest in their manuscripts than men; less likely to be published; less likely to be reviewed or noticed in the media (in 2014, a gender equality research organisation called VIDA found that The New York Review of Books had covered 354 titles by men, and a paltry 164 by women), and less likely to win literary awards (though their chances increase, oh the irony, if they're writing from a male perspective). Even when you reach that great levelling point, the internet sales portal (and despite the fact that the majority of book buyers are women), female authors are categorised in ways that at best demote them, and at worst remove half their potential buying public. Moriarty is a classic example: on Amazon, like many female authors in her genre, one of the places she's listed is in the sub-category of "Women's Literature". (As author Joanne Harris put it in a furious Guardian article in 2014: "Women are not a sub-category!") And then, within that sub-category (which has no male equivalent; there is no "Men's Literature"), Moriarty's works are further marginalised under the heading "Domestic Life". How many men – who often write to Moriarty, and so must, somehow, be getting their hands on her books and reading them – go online to buy a book and think, "Oh, goody. Let's have a look at the Domestic Life list"? Of course, Moriarty is famous enough that her books are all over Amazon – in the mainstream best-seller lists, for example – so she's less affected by this particular bias than many women, some of whom might appear nowhere else. But, like most female writers, she's conscious of the inequities of the system. We spend some time discussing the literary equivalent of a street brawl that began in 2010, when popular US commercial novelist Jennifer Weiner criticised the "Franzenfrenzy" of media attention surrounding Jonathan Franzen's Freedom. How about giving a tenth of that publicity to a novel by a woman, Weiner suggested. Franzen retaliated by criticising writers who engaged in "Jennifer Weiner-ish self-promotion," and the battle has raged ever since. Time seems not to have healed all wounds – or indeed, any wounds at all: last year Weiner called Franzen "the worst internet boyfriend ever", after he accused her of "freeloading on the legitimate problem of gender bias in the canon". Franzen went on to insist that "I know no one, male or female, who says, 'You've got to read Jennifer Weiner' " and "there is no case for why formulaic fiction ought to be reviewed in The New York Times".

The New York Times positively reviewed Big Little Lies in 2014. Moriarty is philosophical – mostly – about the debate. "I'm sure if I was Liam Moriarty I'd be treated differently," she says wryly. "I'd be so interested to see myself in that parallel world, where I'd written exactly the same books, but as a man. Would they be 'unflinching'? I think they would be." She pauses, thinking. "I do remember being infuriated when I saw an article about me with a title along the lines of 'the suburban housewife who became an international sensation'. It was so patronising – and also totally incorrect! It wasn't that I was at home and started scribbling on the side: I had four published books before I became a mother." She smiles. "Adam [Moriarty's partner] found it very funny, because I'm not a very good housewife at all. He kept saying, 'Go and do the ironing!' " But that being said, Moriarty won't be out on the hustings any time soon fighting for more recognition. Her preferred organs of publicity appear to be local libraries, where she and fellow authors Dianne Blacklock and Ber Carroll sometimes give joint talks (Moriarty acknowledges that she is especially motivated if there's a morning tea with carrot cake afterwards). She seems, in the politest way, not to care, really, how the world – aka the literary media – regards her. And you can see her point. As Weiner put it after summarising the criticisms against her: "And now, to go and weep into my royalty statement." Or to put it another way, which Moriarty is far too nice to do: Don't get even. Get rich. One of the things one always wonders about people who become fabulously wealthy is whether it changes them. But apart from the extraordinary house, which Moriarty and her family bought late last year and only moved into a few months ago, her friends say Moriarty is resolutely unchanged by success. Friends often say this, of course, but it does seem true in this case. "She only just got all the dings beaten out of her car," explains Dianne Blacklock. "And before she went to LA, I said to her, 'Come on Liane, you've got to get yourself a decent phone.' Hers was about 100 years old." She was in LA, as it happens, because Nicole Kidman, true to her word, along with Witherspoon and a cast featuring Shailene Woodley (Divergent, The Fault in Our Stars) and Alexander Skarsgård (True Blood, The Legend of Tarzan), have just finished filming Big Little Lies. It will be televised as a major eight-episode series on HBO next year. (Her fifth novel and first mega-seller, The Husband's Secret, has been optioned by CBS Films, and Jennifer Aniston has been linked to a film project based on her third book, What Alice Forgot.)

Moriarty seems delighted by the concept of seeing her story on screen, perhaps because she no longer feels it's hers, so she can be enthusiastic without appearing immodest. She also doesn't seem to have any artistic fears about alterations to the plot or characters. "They offered me the chance to write the screenplay," she explains, "and I quite like, now, the idea of writing an original one. But I think I'd find it a little bit boring adapting a novel I've already written." Instead, David E. Kelley (LA Law, Ally McBeal) took on the task. Still, Moriarty found when she went on set that "whole chunks [of my text] are still there, which was slightly surprising and great". Great – but not something she's been prepared to use as publicity leverage. "You get some authors and you can't shut them up," says Paterson affectionately. "They are consummate self-promoters. But Liane doesn't have a Twitter feed and only an infrequent Facebook presence. The most you can do is say, 'Now listen, Liane, when you go on set, please, please, get a photo with Reese Witherspoon.' " Moriarty did get a photo with Witherspoon. But she was, initially, a bit uncertain about the rest of the cast. "Liane doesn't know who anyone in Hollywood is," says Blacklock. "When I read that Adam Scott [The Aviator, Parks and Recreation] was in it, I texted her saying, 'Adam freaking Scott's in your show!' And she was like, 'Oh, um, really?' She said back at the beginning, when the producers rang her with the cast list, she could tell they were surprised she wasn't more excited; but she didn't know any of the actors' names." She laughs. "But to be fair, last time she was on set, she did text me and say: 'I've just met Adam freaking Scott.' " If Adam Scott had grown up in her neighbourhood, he would certainly have known who Liane freaking Moriarty was. "She was the queen of the family, the storyteller of our childhood," explains her younger sister Jaclyn Moriarty, a highly successful writer of novels for young adults. "All the neighbourhood kids still talk about her to me, actually. You know how you reconnect on Facebook? Well, all those kids, who are now in their 40s, still remember the games she came up with. It was like she was the director of this magical movie. We would run all over the neighbourhood and she would be narrating the story and we would all be characters in it." Moriarty, now 49, is the oldest of six children, five girls and a boy. As Ber Carroll, also one of six, puts it, "with that many siblings it's all happening. There's a great deal of writing material." Even so, it seems extraordinary that three Moriartys ended up as authors – Liane, Jaclyn, and their youngest sister Nicola (who has published two novels while studying for a teaching degree).

"I know!" says Bernie Moriarty, their ebullient-sounding father, a surveyor specialising in aerial photography. "But there was a lot of making up stories when they were little, I suppose: maybe that helped. I was working bloody long hours, and when I came home at night I couldn't bear to sit and read them stories in bed. So we'd do it together. I'd go in and say: 'You start it, and I'll carry on.' So they'd say the first sentence, and then I'd ramble on and send them to space or have a dragon set them on fire or whatever." As well as witnessing these nightly acts of creation, the Moriarty children also had their dad cheering them on in their own artistic endeavours. "I wanted them to earn pocket money, but I wanted them to do something they enjoyed. So they'd write stories, and I'd pay them. 'When they finished one I'd say 'Right, there's your 50 cents. Now, what's the next one?' " It sounds a very happy, albeit busy, childhood – Liane's mother Diane, who adored babies, fostered more than 40 children while Liane was growing up – with strong role models for doing what you love. "Dad did make writing seem like a viable financial option!" says Jaclyn, laughing. As he himself puts it: "I always told the kids, 'If you can do what you enjoy and some bastard pays you, how good is that?!' " Nevertheless, it took Liane a long time to write professionally for anyone other than her father. Indeed, she worked successfully for many years in advertising and marketing after university. And then, one day, Jaclyn published a novel.

Sibling rivalry can be a funny thing. One wonders about secret resentments and steely-eyed competition, but the Moriartys seem both realistic about and unfazed by each other's success. Jaclyn, whose first novel won a NSW Premier's literary award, was once asked at what point she realised Liane had made it as a novelist, and laughed. "You mean," she corrected the journalist, "when I realised she had beaten me?" "I can't really understand why I don't feel jealous of her," Jaclyn says now. "But I don't. She's had hard times, and she's worked hard, and I'm just purely happy for her. I was married to a writer [Canadian Colin McAdam] for 11 years, and people were always asking if we were jealous of each other. But if you love someone, you just feel so happy and proud of them when they do well." Liane, meanwhile, credits Jaclyn with the original motivation for her brilliant career. "I can still remember exactly where I was when I found out she'd got her first deal," Liane says, sitting forward. "I feel like I can see the camera zooming in on me. I was in my office [as marketing manager for a legal publisher], with my shoulder pads, in North Ryde, thinking I was pretty good, and she rang. She was so excited. And I was excited for her. It seemed so amazing: that you could actually get published!" She smiles. "And she's such a beautiful writer: she's never written a boring sentence in her life. But there was the other feeling – sheer rage! No, no – but definitely disappointment with myself, that I hadn't done it and she had."

Two years later, with the help of a creative writing Masters course encouraged by Jaclyn, she'd completed her first novel. Three Wishes, like all Liane Moriarty's books, is set among a group of women in suburban Sydney, without a single sex scene or bewitchingly beautiful heroine or master-of-the-universe hero to be seen. But it's funny, and cleverly structured, and warm – which is a hard quality to describe, but has something to do with optimism, and humour, and fundamental sympathy for people and their flaws. "I never took myself very seriously as a writer," she says now, looking down. "As a kid I just wrote, in this completely uncomplicated way, for enjoyment. And the Masters let me do that again. It reminded me about this whole other level of happiness that I'd forgotten. I think writing doesn't matter – I think I'm not arty enough for it to matter – but it does. I need to do it." She looks up. "In class, we'd read out what we'd produced each week, and people were so encouraging. I can remember coming home and my cheeks feeling still hot because people had been nice." She holds both hands up to her face at the memory. "I felt hot with happiness."

She sold Three Wishes to Pan Macmillan in 2002. Fiona Inglis brokered the deal. "It was very easy: so easy I can't really remember it," Inglis confesses. "But I'm one of three sisters, and Three Wishes is about three sisters, and I remember reading it and thinking, 'Oh my god. She is describing my life.' " The first Liane Moriarty novel I read was The Husband's Secret. I read it before I was assigned this story, and I had no idea who she was. I assumed from the cover – bright colours, cartoon balloon, friendly type – that it was commercial fiction, and as a result I totally underestimated it. Even after I finished it in a single night, and gave it to my intellectual neighbour with an apologetic disclaimer – "it's sort of chick-lit, but for some reason I really liked it" – and she also loved it, I still couldn't quite get my head around what that meant. What it means is that Moriarty's writing is, in fact, more than the sum of its parts. It is commercial fiction, in the sense that it's strongly plotted, with happy endings neatly resolved. ("Not too neatly, I hope!" she cries. "I hope it's not like Notting Hill or something – even I was going 'Stop stop stop!' ") But it contains surprisingly dark elements – damage, death, viciousness – that are deeply unsettling amid the Tupperware parties and banana muffin baking. As The New York Times put it, reviewing Big Little Lies: "The ferocity that Ms Moriarty brings to scenes of masculine sadism really is shocking." But then again, it's not the shock that stays with you, it's the warmth. Weeks after finishing the novels, I was still thinking about their characters as if they were people I knew: "I wonder if Erika's fostered any kids"; "Thank heavens Alice didn't leave [spoiler alert!]"; "God, Perry was such a shit." And this is Moriarty's great skill: creating fictional worlds that feel real. Some of this is fact merging with fiction: she is a mother of school-aged children; she has battled infertility. She has also experienced domestic abuse. The most famous instance of this in her work is in Big Little Lies, in which a loving couple is locked into a sickening – and strangely compelling – cycle of violence. But in her very first novel, one of the main characters has been emotionally abused by her ex-fiancée. "That ex was based on an early boyfriend of mine," Moriarty acknowledges. "He wasn't physically abusive, just a very angry man. But I suppose I've thought a lot about it: if you don't have the physical side, just someone getting really angry, is that okay? And the answer is no." She smiles. "I took great pleasure in killing him off."

As for IVF, she and Adam struggled for years before they had their son and daughter, now aged eight and six respectively. (Moriarty had a marriage in her early 20s that appears, now, to be a total mystery to her. "He should have been just one of those nice-but-not-the-right-person people you go out with.") She met Adam in her late 30s. He's a tall ex-farmer in a checked shirt who puts his glue gun down to shake my hand, makes an excellent cup of coffee and seems unawed by Moriarty's success. "He's Mr Mum," says Moriarty proudly. "He does it all much better than me." She grins. "And he would agree with me about that." "It's a joy," she says of motherhood, "a complete joy. What can you say?" But some part of her – the part that writes, clearly – has never forgotten the bitterness of infertility. Her best characters are those battling procreative demons: they're mouthy and fed up and intensely convincing. "I'd like to write a character who really doesn't want children," she admits. "I don't want people to think I'm suggesting you should have a baby, or that a baby's the only way to happiness." "I'm never trying to make a political point when I'm writing," she adds at the end of our afternoon on the palatial terrace, just before she gives me a ride back to town in her reassuringly non-palatial car. "Except, I suppose, that if I go out with a group of mothers, I'm always conscious that people are looking and thinking: 'Oh, just a group of soccer mums.' We always underestimate each other. But there are always the most incredible lives going on behind the scenes. You only have to walk behind one door and you find a story to tell. That's what I'm interested in." She looks out over the sparkling pool and beautifully groomed tennis court: the behind-the-scenes proof of her own incredible story. Then she looks back and smiles. "As a girlfriend once said to me, most of us aren't on the edges of society, most of us are right in the middle. That's where our stories are happening."