In the warm kitchen of a bungalow just off a two-lane road in far-western Ireland, the novelist Sally Rooney, her mother, her sister, and her mother’s friend were contesting the issues of the day over a supper of pork loin, roasted potatoes, green beans, red peppers, and applesauce. The pace of the conversation was brisk, the threshold for entry high. You had to be careful with the prosecco.

“A Star Is Born” came up. The film’s lone advocate was quickly crushed with an analysis of its gender politics and time-line issues. The discussion turned to Brexit. We were in Castlebar, County Mayo, at the home of Rooney’s mother, Marie Farrell. Everyone was worried about what would happen to the Irish border if the United Kingdom left the European Union without an agreement in place. And what of the Labour Party? Rooney said that although she didn’t exactly love the Labour leader, Jeremy Corbyn, she did want him to become Prime Minister.

I asked what she made of Corbyn’s lukewarm support for Europe in the run-up to the Brexit vote.

“I was Remain, like any sensible person,” she answered.

In “Even if You Beat Me,” the 2015 essay that launched her career, Rooney looked back on her time as the “number one competitive debater on the continent of Europe.” The essay is excellent, but Rooney now sort of wishes she hadn’t written it, seeing it as an inadvertent overshare. “I wrote it with a confident sense of my own anonymity,” she told me. An agent, Tracy Bohan, of the Wylie Agency, saw the piece and got in touch with Rooney. “I said, I know you write fiction as well. Do you have any material you’d like to share?” Bohan recalled. Rooney gave her a manuscript, which, a month later, Bohan sent to publishers. She received bids from seven of them.

Rooney’s fiction is largely concerned with the power dynamics of social groups. Maybe it’s unfair, then, to begin an article about her by citing a stray piece of personal nonfiction. But her acknowledgment, in the essay, of a “taste for ritualized, abstract interpersonal aggression” provides a better insight into her habits of mind than any I could manufacture. I can make a strong case for beginning with it. At the same time, I can imagine Rooney—who recalls having “nursed intense romantic obsessions for droll counterfactuals”—noting the unoriginality of invoking her collegiate debating record as evidence of her verbal precocity. She gets in your head like that.

Thomas Morris, a writer in Dublin, told me that his friendship with Rooney began at a university literary-society event, over a platter of Bakewell tarts. Morris said to Rooney that he’d rate the tarts an eight on a scale from one to ten. She was sure that they deserved a six. Then they started sparring over whether they were ranking the Bakewell tarts as Bakewell tarts or as food in general. “I naïvely, arrogantly thought because I was older that I would win the argument,” Morris said, at one of Rooney’s recent book events. “But you can guess how it went: Sally was right, and I was wrong. And I knew immediately that I wanted to be friends with this person who could so easily upend, and transform, my view of the world—and my ranking system for cakes.”

A lifelong Marxist, Rooney is particularly outspoken about issues that stir her social conscience. Shortly before the publication of “Conversations with Friends,” her first novel, in 2017, a piece about her appeared in the Irish Independent. It began:

Sally Rooney is apoplectic. She squirms in her seat, hands flapping in disgust, and doesn’t mince her words.

“I hate Yeats!” she shrieks. “A lot of his poems are not very good but some are obviously okay. But how has he become this sort of emblem of literary Irishness when he was this horrible man? He was a huge fan of Mussolini, he was really into fascism, he believed deeply in the idea of a ‘noble class’ who are superior by birth to the plebs. And he was in the Senate.

“He wasn’t just this harmless weirdo who wrote poetry. People misinterpret him in this country, and when we’re taught about him in school, it’s just hagiography.”

Rooney’s voice is bright and crisp. There’s something autumnal about her. It’s hard to see how you could characterize her as shrieky, unless you believe that forthright and vigorous speech from women in their twenties necessarily constitutes shrieking. But her criticism of a national hero—and her assumption of the standing to do so—caused a small controversy. “Oh, my God, that was so ill-advised, trashing Yeats!” she told me, seeming more amused than chagrined. The piece made no mention of a scene in the book in which Frances, the narrator and one of a quartet of entangled friends, tells Nick, with whom she’s having an affair, that she recently slept with a guy she met on Tinder. Nick, chopping onions, asks what he was like. “He was awful,” Frances answers.

He told me he loved Yeats, can you believe that? I practically had to stop him reciting “The Lake Isle of Innisfree” in the bar.

Wow, I feel terrible for you.

And the sex was bad.

No one who likes Yeats is capable of human intimacy.

Rooney, with the spoken equivalent of a wink, told me, “I feel like you can really get away with putting a lot of your opinions—if you wanted to—in a novel.”

Rooney, who is twenty-seven, has written two of them. “Conversations with Friends” follows a pair of female college students, Bobbi and Frances—former lovers who are still best friends and collaborators on poetry performances—who become involved with Melissa and Nick, a thirtysomething married couple whose bourgeois life style they find alternately thrilling and pathetic. The book blew away many people, including Zadie Smith, who praised it as one of those “debuts where you just can’t believe that it was a debut,” and Sarah Jessica Parker, who wrote, on Instagram, “This book. This book. I read it in one day. I hear I’m not alone.” The marketing tagline, “Salinger for the Snapchat generation,” was apt in its evocation of freshness, but Rooney is too cool, in both senses of the word, for the description to fully work. Her characters are let down by the adult world, but intrigued, too, and maybe galvanized. Their default attitude is a raised eyebrow. They fear that they might be the biggest phonies of all. The book even looks cool: its bright-yellow cover features an Alex Katz painting of two stone-faced young women, one with red lips and the other in dark glasses.

Rooney’s second novel, “Normal People,” was nominated for the 2018 Man Booker Prize, and will be released in the United States in April. According to The Bookseller, it was the year’s most critically praised book in the United Kingdom. Like “Conversations with Friends,” it is basically a romantic tragicomedy. The point is not so much the plot as the characters, and the heady relationships in and out of which they move “like figure-skaters, improvising their discussions so adeptly and in such perfect synchronization that it surprises them.” In the opening chapters, Marianne, a smart and unpopular high-school student whose single mother is a lawyer, begins a secret relationship with Connell, a smart and popular high-school student whose single mother cleans Marianne’s family’s house. “She just acted the same as always, like it never happened, reading her book at the lockers as usual, getting into pointless arguments,” Rooney writes. One of the unusual pleasures of Rooney’s novels is watching young women engage in a casual intellectual hooliganism, demolishing every mediocrity that crosses their paths, just for the fun of it.

The quality of thought eliminates the need for pen-twirling rhetorical flourishes. Rooney’s most devastating lines are often her most affectless. In “Conversations with Friends,” a party at Melissa and Nick’s is “full of music and people wearing long necklaces.” Read that sentence and you may never want to wear jewelry again. In “Normal People,” Connell abandons Marianne, fearing the judgment of his peers if they find out about the relationship. He quickly moves on to the queen bee of the class, less out of enthusiasm than out of a passive acceptance of his social predestiny. “He and Rachel started seeing each other in July,” Rooney writes, in the close third person. “Everyone in school had known she liked him, and she seemed to view the attachment between them as a personal achievement on her part.” A mean girl is no match for an incandescently intelligent one.

Rooney pulls and twists sentences as though they were pieces of balloon art. Words are her superpower, but she is suspicious of them. In “Even if You Beat Me,” she writes about having to extemporize on “the secession of Republika Srpska from Bosnia and Herzegovina” in front of a group of Serbian debaters, and being unsettled by “the composed self-assurance with which we fabricated the history of their region.” She eventually quit debating, finding it “vaguely immoral.” She’s not much more convinced about the social value of the novelist. “There is a part of me that will never be happy knowing that I am just writing entertainment, making decorative aesthetic objects at a time of historical crisis,” she told the Irish Independent.

The day after the supper in Castlebar, Rooney and I took the train to Dublin, where she lives. We sat facing each other across a table. The night before, she had mused aloud about her attitude toward interviews. “There are two warring aspects of my personality,” she said. “One of which is a desire to be friendly and nice, because I know journalists don’t love you to give monosyllabic responses. The second is: don’t tell them anything.” Now she had a question for me. She asked it politely but seriously. Why did I think that a profile of her was worth writing? If this were a debate, the motion might have been: This house, while honored, fundamentally believes that we are wasting our time.

I said that I thought her books meant a lot to readers, who would understand them better by hearing what she had to say. I brought up something that she had written on Twitter, before she temporarily shut down her account: “novelists are given too much cultural prominence. I know you could point out they’re really not given a lot of prominence but . . . it’s still too much.” I didn’t necessarily agree, I said. I rambled a little.

Rooney leaves you with a lot to think about. Your esprit de l’escalier doesn’t kick in until you’re well out the door. When she was a teen-ager, she joined a writing group at a local arts center. One of its organizers, Ken Armstrong, said that, even then, there was “a thread of steel running through her.” I wanted to know where Rooney got her mettle, how a Marxist ended up writing a book that sits alongside body lotion and silk pajamas in GQ’s “30 Fail-Safe Gifts for Her” guide; how she upended the conventional wisdom that a writer should show and not tell, that characters shouldn’t say what they think, in the process creating some of the best dialogue I’ve read. There is a quiet but insistent sense of challenge in her writing. It makes you wonder whether you’re wearing the moral equivalent of a long necklace.