I should stress at this point that what he's actually doing is illustrating the core psychology of the participants in the American Civil War. A tribal atavistic desire of sadistic one-upmanship which lies at the heart of his new novel Redemption Falls. It's his follow-up to his incredibly successful Famine novel Star of the Sea, a book that received the blessing of no less than Richard and Judy, and which went on to give O'Connor his first number one best selling book in Britain.

It was what he calls a "fantastic experience" and he wishes "the happiness of that moment could happen to every author once".

You get the impression that he's looking forward to the release of Redemption Falls, not in the way of a man with arrogant and over-inflated expectations, but in the sense of someone who is now pleased with his command of his craft. A craft he perfected with Star of the Sea and that he has taken a step further with the almost profligate ambition of the devil-may-care fall-on-your face narrative ambition of Charles Dickens and George Eliot. He views it as a kind of jump from the creative precipice.

The result is an epic story set in the aftermath of the American Civil War examining the lives of a cast of characters which includes ex Irish rebel and reluctant governor General Con "the Blade" O' Keefe, his wife Lucia, a young girl called Eliza Mooney in search of her young brother, a sneeringly villainous cartographer, the brutal outlaw Johnny Thunders, and a host of others. It's a grand polyphonous canvas that recalls the form of Star of the Sea, yet it is resolutely different in tone and subject matter.

O'Connor is now at that unique juncture in his career where he has managed to achieve both popular and critical acclaim, and although he doesn't allude to it, Redemption Falls will be pored over by some for any chinks in his literary armour. Despite this weight of expectation he seems calm and content, exuding the relaxed demeanour of someone who knows he's about to be the passenger on a very interesting journey.

"I don't allow myself to feel those expectations. I just wrote the book I wanted to write. That's how Star of the Sea came about too. If I'd listened to expectations then I never would have written a big 400-page novel about the Irish Famine." Thanks to Star of the Sea he now has a very clear sense of where his craft is going as he talks about his growing confidence. "This is my sixth novel and my 13th book, so I don't believe I'm absolutely shite. My first couple of books I probably thought, Jesus, I'm really getting away with it. But I think with Star of the Sea I learned an awful lot about how a novel works. I think it was the first time I ever really got inside the architecture of a book and I felt that I was really controlling what happened."

This control and poise is underlain by a simple philosophy which prevents him from giving into commercial considerations and compromising himself artistically. Instead he believes that "you should always write the book you want to write. If you do what you want to do and do it as well as you can then the book will find an audience."

This attitude has served him well in the creation of Redemption Falls, which, while stylistically resembling Star of the Sea is no formulaic re-tread, but rather an evolution of the technique and approach he brought to that novel. He has always been a writer driven by his enthusiasms, whether it be his affection for London in Cowboys and Indians or his interest in Nicaragua in Desperadoes. This time around O'Connor's main fascination is with language, and his attempt to create something that is "rich involving and pleasurable". He talks enthusiastically about the various dialects in the book, the Louisiana patois, the use of Irish language, the slang words born of the marriage of different cultures, and while rejecting my various attempts to reduce the novel to one theme he concedes that its overall vision may have something to do "with the language in which the book was written. That at least when things are awful, at least in the midst of a war, if something as beautiful as American English is forming itself, it means that there are other zones of solidarity and we can escape from the prison of national tribal vanity.

And at least this beautiful thing, this beautiful operatic, symphonic language that we use every day, at least that is here and that's the point of the book, if indeed it has a point."

Of course the one inescapable thing about the book is its wartime setting and by natural extension its bleakness. While it may seem unremitting to some, O'Connor believes that it is all rescued by the book's close.

"There's a revelation in the ending which tilts the bleakness into being a story of love and survival.

You realise at the end of the book that at least one good thing happened." Meanwhile, he hopes the barbarity is also leavened by "moments of intimacy" and he talks openly about the paradox of writing a war novel with a lightness of touch. "For a novel to work it has to be a very playful and intimate thing, that goes all the way back to our childhoods, which is that we like to be told stories, we like to step out of what we are at the moment. All stories work by empathy. The whole range of storytelling is about that.

It amounts to whether I can make you enter somebody's head for a brief defined time." It's this emphasis on playfulness which seems to have defined O'Connor the writer since Star of the Sea, enabling him to up his game and deliver satisfying work of real magnitude and intensity.

He has a very clear vision of what writing this book entails and of how the subject matter has informed its sprawling multivoiced quality: "If you're doing a book about a war . . . if you're going to do it properly, and if you're going to do it in a way that's true in any way to the historical background . . . it has to be big. It has to have conflicting voices and perspectives, because there is no one real version of war. Any novel that doesn't reflect that self-evident reality I think is suspect, and is just using war as a backdrop or as an engine for the plot."

Ironically, given the historical settings of his own work, O'Connor confesses to having a certain distaste for the historical novel, revealing that he really doesn't actually like the genre, particularly because he doesn't subscribe to what he calls the "this happened and now it's over" school of historical thought. You get the feeling that he sees this as a major failing both in fiction and in actuality. In fact for him the repercussions of the American Civil War have reverberated through American culture for generations, informing the south's dislike for the "wealthy northern liberal" in the form of a poor unfortunate like John Kerry, and the silent bigotry that may yet scupper Barack Obama's hopes of becoming president. But in the end he returns to the world of the historical novel rationalising its worth when he says "I sometimes feel only people who dislike the genre should be allowed write in it because it gives you the freedom to take it apart and put it back together again in new ways."

He's also not averse to the current trend for reading everything with any kind of military content as some form of allegory for Iraq.

If this book didn't have contemporary resonances then he would be disappointed. It's hard not to read the chaotic opening chapters with their cinematic vision of a shattered country now trying to find its feet as something which recalls the current post-war chaos in Iraq. As he puts it, "I wanted this to be a novel, where, if it's about war . . . which it isn't . . . then it's about all war, it's about war now, it's about war then."

He stresses his quest for realism and truth in expressing the real horror of war and his dislike for the old-school sentimental novelistic version of war which has brothers on opposing sides finally hugging and returning to the golden pastoral tranquillity of their farms. He believes that we in Ireland know the truth that civil wars never really end, "they just change shape".

You sense that he's proud of the book and rightly so. Indeed there are moments of sustained brilliance such as the chapter detailing O'Keefe's desertion on an island (his response to "the classical imperialistic text that is Robinson Crusoe") which in its psychological truth and realism makes Daniel Defoe look like a literary amateur. He likes writing novels, even though he wryly admits that "it's a terrible way to spend your time".

Nevertheless, he will continue.

He has an idea for another novel, a short one with a single voice, "chronological and very simple, just a voice of a woman telling a story". It will help him finish the final third of what he sees as one large story which began with Star of the Sea. He'll probably write it in Dublin. He's settled back here with his wife and two sons, and he carries himself with all the contentment and ease of a man whose personal and professional life is blossoming. He's lived in London, Nicaragua and has been guest of the Cullman Centre for Scholars and Writers which allowed himself and his family to live in Manhattan for 10 months. It was a sojourn which helped him to research and write his book. He's spoken before about his great affection for big cities and the energy and life they possess, yet for all his semi-nomadic wanderings you get the impression that this stay in Dublin may well be a long-term one this time. It was in Dublin where it all began for him, and he speaks fondly of his time here as a journalist and of how it was time well spent which helped open his eyes both culturally and politically.

For now Joe O'Connor is a man who looks like he's setting out on a different type of journey, and one that started in the very pages of the Sunday Tribune when his first short story was published in the New Irish Writing columns. It was enough to convince him that writing stories was what he wanted to do. As he says "I wouldn't be here today talking to you about my novels if it wasn't for one man. I have Ciaran Carty to thank for everything. In fact, a lot of people do."

Redemption Falls is published by Harvill Secker on 3 May