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 leans back with a hearty laugh as if bemused by her own ire. I consider interjecting on behalf of the 1923 Nobel Prize-winner but think better of it. For one thing, we're here to talk about Rooney finding herself as Irish fiction's white-hot hope of 2017 following a seven-way bidding war for her debut novel, Conversations With Friends. But besides all that, she is also a former European debating champion. You pick your battles, as they say.

"A lot of people ask me did debating help me as a writer and I honestly don't know," Rooney wonders, her voice all sing-song curiosity. "It was good for me because I got to meet people from Harvard and stuff, a class of people that, being from Castlebar, I didn't have access to offhandedly. So that experience of being a fish out of water but feeling I could beat these people at their own game, that definitely feeds into the novel."

Debating was also, she says, a way for her 18-year-old self (the only girl from her school to go to Trinity) to achieve popularity in a new environment. Her logic was that the most popular person in the sports club was the one who's best at the sport.

"I was a bit lost," she shrugs. "I think the debating thing actually helped to establish to me that being popular was completely worthless. I didn't enjoy the social dynamic and immediately left after becoming number one. But it felt like I needed to do it to know what it was like. It wasn't just that I was an aggressive person, although that probably is true to an extent."

While formidable - a debating partner once described her as "eerily clever and stunningly eloquent in equal measure" - you wouldn't call Rooney aggressive today. In fact, she is a barrage of mirth, grace and self-deprecation, with shyness hovering somewhere about her. As Conversations With Friends, clothed in swooning blurbs from Lisa McInerney and Sara Baume, prepares to hit the shelves in 13 territories, all this new-found attention is stressful, she chuckles.

"It has no seeming relationship to what I am actually good at," she moans theatrically. "Why I'm here is because I spent a year-and-a-half writing a book on my own in my room just not speaking to anyone. And now I'm having to engage and perform a kind of public persona. There's elements of it that are kind of exciting but it's also incredibly draining because I'm naturally an introvert."

Hang on. Hasn't she won awards for standing in rooms full of strangers speaking at the top of her lungs in passionate tones? "That's completely different though," she says, batting the theory away. "It's abstract. If every interviewer wanted to ask me about the new National Maternity Hospital, that's fine. But people want to know about my life, and I have no practice speaking about these things, never mind to complete strangers!"

This complete stranger will get to St Vincent's, but first she is duly asked to practise speaking about said life. It turns out she's not bad at it, describing growing up in a book-filled household of five in Castlebar. Her father worked for Telecom Éireann while her mother runs the Linenhall Arts Centre. Both are "big readers" and were supportive of the young Rooney being always buried in books. What do they make of all this?

"My mum has obviously always been around artists and writers," Rooney smiles, "so for her, it's not like, 'wow, someone's written a book.' My dad is more bemused. He's quite introverted like I am. I told him I was doing this interview and he was like, 'I don't envy you!' They're a bit surprised this has all happened so quickly, but yeah, they're very proud." Although always very academic in school, Rooney was never pushed towards a safe and secure professional direction by them and feels very lucky about that.

Appearances in journals such as The Stinging Fly and Granta displayed a flair for short stories (she was shortlisted for the £30,000 Sunday Times EFG Award this year). She finished her first draft of Conversations... three years ago after one short story refused to have its themes enclosed within a word count.

It is easy to see why there was such a scrum over it. With wisdom and a pronounced level of observation, it tells of Frances, a 21-year-old Trinity student and our narrator. She and Bobbi are former lovers who remain inseparable as they go about college life. They meet an older, petit-bourgeois married couple comprising journalist Melissa and actor Nick and become enamoured by a world of leafy Dublin suburbs, avocado toast and holidays in Provence. Frances knows much but understands little, and when she embarks on a sweltering affair with Nick, her deep connection with Bobbi is knocked off kilter. A television adaptation feels inevitable.

Frances is in her early twenties and reads English at Trinity. Her parents live in Mayo. Sounds familiar, I comment. Rooney unfolds herself from a vigorous belly laugh and agrees that it is, of course, all about her.

"Writing in the first person, you immediately open yourself up to the idea that there's a connection between you and the narrator. I don't know what to do with that. I feel like I should have a more sophisticated response but I can't say absolutely zero per cent of this book is from my life because it so obviously isn't - even reading the little bit on the back, it's clear some of the details align. But then, equally, none of this happened to me."

Another characteristic that she shares with Frances is her politics. Rooney outlines in no uncertain terms her arguments in relation to issues such as capitalist structures, the wealth gap, environmental destruction, St Vincent's, abortion and church-state dynamics, all unsurprisingly streamlined, robust and propelled by a genuine concern.

Between this and her wish to be writing novel number three in five years' time, you can sometimes forget that Rooney is barely 26. The effect isn't helped by her vow to "always write books" even if her debut and its successor turn out to be "huge failures" and she has to go out and find work teaching. "It's not a career in the sense that it doesn't depend on me being able to make money from it. So, it'd be nice if the books kept being published but I'll keep doing it anyway."

Before we go, there's time for lighter subject matter - her love of Italian food, "carbs" and her luck in finding a boyfriend who is an "amazing cook". Once the belly is satisfied, she might listen to some Belle & Sebastian or jazz greats such as Miles Davis or Chet Baker. Like Yeats, Davis and Baker were not particularly nice individuals outside of their artistry, I offer.

"Yes, but they were not fascists, though. Crucially," she fires back without missing a beat.

Spoken like a true champion.

Conversations With Friends is published on June 1 by Faber & Faber

Indo Review