Anne Rice was 34 when she wrote Interview with the Vampire, set in her native New Orleans, and as far as she was aware, the only book of its kind to be told from the point of view of the vampire, not the victim. She was a graduate student, an insurance claims processor and a writer who had not published anything. And so, although it was the 60s and everyone around her was "dancing in the streets and drawing on the pavement", she sat down to do something very square indeed: produce a novel.

Forty years later, Rice is in the living room of her estate in Palm Springs, two hours east of LA. Outside, the pool area, with its imported 100-year-old olive trees, acts as a buffer against the scorched desert air; inside, 8,000 square feet of sumptuous decor and quirks of taste, such as her collection of saints on a shelf in the vast, marble kitchen. Rice once had 49 staff, which you can when you've sold an estimated 100 million books, starting with the Vampire Chronicles, diversifying into angels, and with two, apparently contradictory sidelines: erotic novels (from Exit to Eden: "He kisses the way I imagine men kiss each other, rough and really luscious . . .") and a two-volume life of Jesus, written in the first person ("I am Christ the Lord . . ."). Her recent, angry split with the Catholic church made as much news as her sales figures, and she once turned up to a book-signing in a coffin. Still, on the surface, she is tidy, precise, not remotely rebellious. For 41 years, she was married to her high school sweetheart, Stan. "My behaviour has always been ultra-conservative," she says, "but my imagination –" she smiles "– is just rampant with mavericks."

The latest book, Of Love And Evil, is the second in a series about Toby O'Dare, a former assassin turned envoy for angels, who time-travels to Renaissance Italy like a kind of celestial MacGyver. It will, she says, be reviewed through the prism of her fallout with the church, but she can't edit her thoughts to suit others. "I think I was brought up with the idea that an author has to follow her own instincts and protect her work. I think that was a given of the 60s and 70s, a romantic concept of the artist that you go with your deepest instincts about what you're doing. I don't think I've ever abandoned that idea. People write to me every day asking for advice, and the most frequent advice I give is have the courage to stand by your work and protect it." I would not like to get into a fight with Anne Rice.

Tom Cruise and Brad Pitt in Interview with the Vampire. Photograph: Film still handout

And she has picked some big fights. Whereas most writers are grateful to be taken up by Hollywood, when Tom Cruise was cast in the film adaption of Interview, she blithely questioned his suitability, queried whether he had read the book and said: "He is no more my Vampire Lestat than Edward G Robinson is Rhett Butler." When her novel Blood Canticle was slammed by anonymous reviewers on Amazon, she did the thing you are not supposed to do: logged on and answered back, with imperious fury. "Your stupid, arrogant assumptions about me and what I am doing are slander."

And now, the Vatican. Earlier this year, Rice, who was raised a Catholic, lost her faith and returned to it in middle age, posted a message on Facebook. "I quit," she wrote. "In the name of Christ, I refuse to be anti-gay. I refuse to be anti-feminist. I refuse to be anti-artificial birth control. I refuse to be anti-Democrat. I refuse to be anti-secular humanism. I refuse to be anti-science. I refuse to be anti-life. In the name of Christ, I quit Christianity and being Christian. Amen."

Given the unchanging nature of the Catholic church, the obvious question is, what took her so long? "Yes," she says, carefully. "I'm still stridently criticised by Catholics who say, you should've known, when you came back. But we all learn; isn't that part of life, that you learn? I joined with the best of intentions, thinking I knew this religion from childhood, thinking it's a fine religion, an honorable religion. Then I began to really study it and I found it was not an honorable religion, that it was not honest. Now, someone else, maybe, would draw totally different conclusions. But I think the argument that I didn't have a right to change my mind is absurd."

Attending mass became stressful. She had a terrible row with a priest friend. "He said Obama was just as bad as Joseph Stalin because of his allowing abortion. And I said, 'Are you seriously saying that? Do you know who Joseph Stalin really was and what he did?' And he wouldn't back down and there was no more discussion."

For years, she thought, if she studied the Bible hard enough she might work out the contradictions. "But then, as I increasingly saw what I thought was sophistry and lies, I thought: 'I can't abide this.' I can't remain with this. This is crazy. There is no basis in scripture for any anointed hierarchy, let alone a male hierarchy. It's just not there. And how in the world did this man-god die, preaching against the temple, and then we wind up with St Peter's in Rome? How did that happen? There were so many issues where I thought the church was flat-out immoral. I had to leave."

Rice's interest in the gothic stems from a childhood spent reading Dickens, the Brontës and ghost stories from the New Orleans public library. "I am the product of New Orleans," she says, and is amazed that everyone who grows up there doesn't become a writer. As a child, she wandered the streets marvelling at the old French buildings and "wanting to capture the atmosphere I sensed; wanting to write creepy, horrible, wonderful stories and scare people and so forth". Her mother took Rice and her sisters to the cathedral and museum and encouraged them to believe that they might, when they grew up, quite possibly be geniuses.

Anne Rice with her husband Stan and son Christopher, 2000. Photograph: Bevil Knapp

She was, says Rice, "a wonderful person", but also an alcoholic who, when Rice was 14, died of an alcohol-related illness. It started during the second world war, when her mother was left alone with two small children and "would take a drink to get the courage to check the backdoor". As a child, when she found her "completely passed out" when she got home from school, she assumed she was ill. This went on for years. "We would say she's sick. She's in a trance. I remember being very little and thinking, 'I wonder if she's drunk?' And then thinking, 'Oh no, that's ridiculous – but imagine how interesting that would be if that was the reason?'" The family – her father was a postal worker – never talked about it, save for a last-ditch effort to get her to AA or hospital. "But these things didn't come to anything. It destroyed her life. If I could go back and take her to a 12-step programme, I would do it. My mind is very much focused on how I wish I could have saved her."

Rice and her husband Stan would go through a lesser version of her mother's experience in the 70s. The two met in high school; Rice remembers the first time she saw him: "His babyface. He was very cute. And very smart. And I was just kind of amazed by him." They got into an argument about religion, the teenage Stan a "ferocious atheist" who informed the pious schoolgirl that, "If Adam and Eve had existed their children would have been idiots within so many generations of inbreeding." She smiles at the memory. "And I said, that's ridiculous. If God can make the world he can solve that problem, what's wrong with you? There started the 41-year argument that never stopped. I loved him right away."

Stan, who died of a brain tumour in 2002, became a poet and college teacher and later, a painter. When she started writing books, he was his wife's first reader. She didn't always act on his advice – Rice doesn't, as a rule, much welcome editing – but he was in more important ways a mentor to her. In 1979, they made a joint decision to stop drinking. If they hadn't, she says, "I probably wouldn't be alive." It was a reaction not so much against the 60s, as the 50s and, "those role models of ours who'd been destroyed. The vision of Faulkner with a bottle of whisky on his desk, drinking himself under the table – we really didn't want to die like that."

Their first child, Michele, died of leukaemia in 1972 at the age of six. It was in the years directly after that Rice began writing. She had a stack of short stories and half-finished projects from her 20s, among them a fragment that would become Interview with the Vampire. The hard work wasn't an attempt to deal with the grief, she says. "No. It was really a desperate attempt to be somebody. I looked around after my daughter's death and realised I was nobody and nothing. I wasn't even a mother any more. I had nothing." The novel was published in 1976 and the couple's second child, Christopher, born two years later, was their real incentive to stop drinking. But it wasn't until 1986, and a novel called the Queen of the Damned, that the family's life really changed. It got to No1 in the New York Times bestseller list and earned back its advance in a couple of days. Rice was sufficiently beneath the radar for editors at the paper to ring up bookshops and ask who the hell she was.

The writer as rock star is often an awkward fit and in the early days of her fame, Rice was terrifically uptight about being taken seriously. When a TV station asked her to interview a vampire onscreen, she threw up her hands in disgust. "Now I wouldn't care; I'd say, 'Of course, darling.' But it took a while for me to realise that there was a lot of fun to be had, if you just relaxed." And the money kept pouring in. She and Stan bought properties in New York, Florida and New Orleans, including a building that took up an entire city block. Still, it's hard to imagine the need for 49 staff. "They were repair men, security people, a staff that ran the building and opened it for fund raisers and weddings. Housekeepers, secretaries, assistants; then I had another house, on the parade route, that I used for Mardi Gras and for guests, and they all had staff. Then I had drivers. I don't drive and never have, and I had a limousine. A lot of the people on staff were my cousins and relatives. It was fabulous. A great adventure."

The success of Rice's novels is in their combination of loopy fantasy and the solid, technical underpinning of conventional storytelling: thematic coherence, good characterisation. She is delighted by the resurgence of interest in the vampire genre – prefers True Blood to Twilight, which she says "is for kids" – and hopes that HBO might make a series out of her back catalogue, or another film. She ended up loving Neil Jordan's Interview with the Vampire, and Tom Cruise. He rang her five minutes after she put down the phone on Jordan, having raved about the film, and was very gracious, she says; he didn't bring up "anything unpleasant". For all her religious scepticism, Rice is generous on the subject of Cruise's Scientology, which, despite numerous attempts by journalists, she has the good sense not to ridicule.

Looking back, she sees her vampires as metaphors for outsiders to the faith, although she was an atheist when she wrote them. "I only saw that as I went on – how fascinated I was by outsiders. I think you discover those things. If you aim for authenticity, if you aim for intensity, a deep excitement, you don't have to say I think I'll write about vampires because that's a philosophically rich concept. You just think: what does it feel like to be immortal? To go into an all-night drug store when you've been alive for 200 years? What do you see when you look at packages of shampoo in all these colours? Everything will take care of itself if you keep digging deeper, and going where the pain is and where the pleasure is."

Speaking of which, the hardest thing to reconcile with Rice's public persona and (sorry) Republican wardrobe, is the racy novels she wrote under a series of pseudonyms, all S&M and people being startled from behind by large phalluses. Rice laughs. "It's probably because of some kind of deep split in my personality. Also, I believe sex is good. That's something I've believed since I was born. I've always been at war against those who don't."

But she's a Catholic! Where's the guilt? "Oh, I have the guilt. But I also have that part of my mind that won't tolerate it. And it keeps reaching for an ideal where people can love one another and be free of constraints. I've always had gay characters in my books with no effort or plan. They just happen. Characters fall in love with people of their own gender or the opposite. Very early on I was surprised to discover that I had a large gay audience, and a faithful gay audience. They kept my books alive in the beginning when they might have gone under."

Her own life, now, is very well regulated, with no real room for romance. After Stan, she can't imagine meeting somebody else. "I don't even know what it would be like to be romantic or familiar with another person. I've no idea. I married when I was 20. I have no idea how to date. But I don't think anyone should ever close the door to that. It could happen. "

It would have to be someone who respected the primacy of her work. She will return to the angel series, Songs of the Seraphim, when the fuss over her walkout from the church dies down. In the meantime, she is still interested in religion and gets up every morning to read "dense" exegeses of one kind or another, like eating kale for breakfast. She is prolific on Facebook and is about to move to a smaller property. And she is working on another novel, about "immortals who've been on the planet since before the fall of Atlantis". So there is reading for that. "My brain is steaming," she says, and smiles. "I'm seeing it all from my point of view."

Of Love and Evil is published by Chatto & Windus on 4 November, price £12.99. To order a copy for £10.39 with free UK p&p go to guardian.co.uk/bookshop or call 0330 333 6846