Dylan Moran: 'I am a bit of a bumbling man, as you can tell..."

For a curmudgeon, Dylan Moran is doing quite well. He's had a long chat in the street with a guy he clearly knows – extremely long, actually, I can feel our precious time ticking away – and now he's got us both coffees, and he's sitting in front of me, all wide-eyed attention and tousled Irish charm. He has, unfortunately, insisted that we sit outside, what with the chain smoking etc, and although a Soho pavement cafe sounds like the perfect place to muse on life and literature and Don DeLillo, as we do, it is, in practice, a bit like sitting at the intersection between the North Circular and the M25, and so we have to shout over juggernauts, and passing nutters, and sirens.

And the gentle, ambling style of his responses doesn't lend itself to shouting. If Dylan Moran is a curmudgeon, he's not a shouty one. He's a quiet, mumbly, muttering-into-your-drink kind of one. But he's not a curmudgeon, of course. To say he was would be to say that Ian McKellen is remarkably like a wizard, and Alison Steadman like a drunken, suburban housewife, and Michael Sheen like a New Labour politician. Because the thing Moran does, in Black Books, the TV series that brought him to a mass audience, which he co-wrote and starred in, is this thing called acting, and the thing he does in his stand-up, which sometimes bears an uncanny resemblance to the doom-laden bookseller who won the heart of a nation (or at least of a discerning sector of it) is also a kind of acting. Because the figure that wanders onto the stage, clutching a drink and a fag, and looking a bit dishevelled, is not (although everyone seems to think he is) Dylan Moran, but a carefully crafted version of him.

Anyway, Moran doesn't clutch the drink and the fag any more. "It goes back to being 19," he explains, "and trying to get on a stage for the first time, and it was in a pub and there was no lamp-stand handy to walk on with, so you took a drink. I used to smoke on stage, too, and I couldn't believe how stupid that was, because it just interrupts the rhythm. When you see a No?l Coward, they just pick it up and go "really" and then sort of store it away again, and that's all written into it. It's a very long answer," he adds (and I've missed out most of it). "You're going to get a lot of those."

But this, it turns out, is just the start of it. There's much, much more on cigarettes, and props, and timing, and the old acting style of a Richardson or a Gielgud versus the ubiquitous documentary style of reality TV, and there's a great disquisition on Pinter's No Man's Land, and how to manipulate timing, and inflections, and the "huge armoury of mannerisms they have at their disposal", and several things are instantly apparent. One is that Dylan Moran is hugely thoughtful, another is that he is hugely intelligent and another is that he is very, very different to the floundering figure on stage. "I am a bit of a bumbling man, as you can tell," he says. No, actually, Dylan, I can't. "Well," he says, "I'm organised in some ways, but not in others. Years ago," he adds, "when I went on stage, somebody shouted out 'Big Issue!'. But then," he admits, "that was useful to me, because that set certain expectations that I can knock down like skittles whenever I want."

He has, in fact, been knocking down skittles for quite a long time. He started at school, in County Meath, but then left at 16 with a leaving certificate and little else. After four jobless years, "drinking and writing bad poetry" – this, after all, was pre-Celtic Tiger and pre-Celtic Tiger collapse – he saw Ardal O'Hanlon perform at Dublin's Comedy Cellar, and decided to have a go himself. A year later, in 1993, he won the So You Think You're Funny award at the Edinburgh Festival. Three years after that, he became the youngest person ever to win the Perrier Award. (He said it should have gone to Bill Bailey, later his co-star in Black Books, and a man who describes him as "a real, old-fashioned wit in the Swiftian mode".) He did his first major tour, Gurgling for Money, in 1997.

The following year, he took his first TV role, in the BBC2 sitcom How Do You Want Me? The year after that, he had a cameo part in Notting Hill, and the year after that he grouched on to the small screen as Bernard in Black Books. It won two BAFTAS, and a cult following, but he decided to kill it, after three series, in 2004. That year, he also starred in the zombie rom-com Shaun of the Dead and it began to look as though acting might take over from comedy. For whatever reasons, it hasn't. Moran's stand-up tours – Monster I, Monster II, Like, Totally and now What It Is – are hugely popular. In 2006, he was ranked by a Channel 4 poll as the 17th Greatest Stand-Up. In 2007, Le Monde named him "the greatest comedian, living or dead".

That, to be honest, might be pushing it, but what Moran does have in performance is an acute eye for the universal and a linguistic precision that verges on the poetic. He is, as the late Miles Kington once said in this paper, "all charm and word magic". Charm, word magic, artful dishevelment – and, well, art. Because that's what it is, isn't it? A kind of art? "Well, you know," says Moran, in full, Irish mode, "I wouldn't run away to the hills with that entirely, because I have hours and hours of material that I've written and some of that I know is good to go, and some of it is not. It's like an endless stew, or compost. I am constantly shovelling new bits in and then old bits get displaced. That way," he says, taking another deep drag of his cigarette, "I don't get bored."

It seems to me, I say, a bit like putting together a poetry collection, where some poems fit and some, you find, don't. Not like writing a TV sitcom, or a novel, where structure is all. And, by the way, he's said he's writing a novel. Is he? "Somebody asked," he says, "and I foolishly admitted it. It was silly. I don't know if there's any point in talking about it." Salman Rushdie, I tell him, once said that "writers are people who finish books". Moran laughs. "But no," he says, "I am publishing a novel, next year". Oh right! So, he has finished it? "No, I haven't." What's it about? "Well," he says, "I'm not sure which one I'll do." Gosh. So not all of this laid back languor is affectation.

"I think," he says, clearly wanting to get off the subject of the novel, "that the thing a stand-up show probably resembles best is a conversation." Hmm. But it's a monologue! "Yes, I know," he says, "but if it's working, you don't feel like that. If you're used to one person talking, you can have a conversation with somebody's reactions and expectations to what you've just said." Well, of course he comes from a nation of storytellers, raconteurs and poets, a country where everyone, it seems, is Seamus Heaney's cousin. You can sit in a pub in the middle of nowhere, as I've done, and meet someone who doesn't just read poetry, but publish it. And the talk! And the charm!

"Charm is interesting," he says. "My wife said 'it's just people lying to you'. I think in Ireland, you're talking about people who all enjoy talk. Subject matter can come down very low in the list of priorities. People style their talk. They work on it." He too grew up in "a very talky atmosphere", one in which books played "a big part". He wasn't too hot on school attendance ("either sick or pretending to be sick") but he devoured the children's classics, "thousands of comics" and a lot of plays. He's still an obsessive reader. So who does he really love?

"There's always," he says, lighting another cigarette, "a host of voices you're inspired by. I love Don DeLillo, and I love Isaac Bashevis Singer, and I love Beckett, and I love Pinter. He's one of the funniest voices in English literature since Dickens. I read The Homecoming again recently, and it's a savage, shocking play." Yes. There's great darkness, in fact, in all the writers he's mentioned. Is he ever tempted to go a little darker in his own work?

"There's darkness in there!" he says, I think a little affronted, "but there's only a certain amount of deliberation that you can successfully carry off, because the light changes, the weather changes. If you're watching a film by Michael Haneke, you feel not just dislocated, but afraid in a way you haven't since you were a child. That's very powerful stuff, and you wouldn't want to be sprinkling that all over your show."

No, perhaps not, but maybe a little bit more wouldn't go amiss. But now he's off again, on S J Perelman, the writer at the New Yorker, and his "great marriage of high and low", and H L Mencken, whose description of Baltimore in the 1880s includes a reference to men with "shoulders like the Parthenon", and Chesterton, who "can be really funny", and Flaubert, and Orwell. It's dizzying stuff – intoxicating, actually – and I find myself wishing that more of this made it into the shows, which sparkle, they really sparkle, but they don't sparkle with this.

I stare at this clever, charming man, with a brain that's a cross between a steam train and a butterfly, and a silver tongue that's been dipped in speed, and piercingly intelligent eyes, and (artfully?) uncoiffed hair, and wonder how on earth he keeps himself stimulated, how on earth he sets himself new challenges. "Well, actually," he says, "there's another Irish theme, that you have to be ashamed if you work for anything, but I worked like a bastard on this show for many months, and looking back on it now, there's less words, and more physicality, because that's an important part of conversation as well."

It's rather hard to imagine Dylan Moran with "less words". Actually, I wouldn't want to. Because it's rare to meet someone who turns a conversation in a café (with juggernauts and sirens) into an art, and who turns conversation on a stage into an art, and who turns random, butterfly musings into an art, and who will no sooner raise a point than argue against it. "I'm fascinated," he says, "by how you'll change your position so many times over a lifetime, but really what you're doing is occupying a series of positions on a landscape."

For some reason, I think of Easter Island. And then Easter. And then the Catholic Church. And then Ireland without a Catholic Church. But that's the thing about Dylan Moran. Once you've heard him talking, you can't switch your brain off.

'What It Is' is at the Apollo Theatre, London W1, from 26 October to 5 December ( www.nimaxtheatres.com ). The live DVD is released on 23 November