Portrait of the artist: JP Donleavy

At 87, JP Donleavy still knows how to entertain, even if these days the party is likely to be in the kitchen of his Mullingar mansion, where it's warmest. The kitchen table has been laid with a set of blue and white china and tea is on the way, but first Donleavy wants to build a fire. He's worried that the house is cold, and it is, freezingly so, with room after shuttered room exuding damp. Levington Park, a vast house with, Donleavy boasts, 11 bathrooms and an indoor swimming pool, has been his home since 1972, bought with the proceeds of The Ginger Man , the cult classic he wrote nearly 60 year ago, which has never been out of print.

But first the cold. There's a fireplace in the kitchen, which Donleavy feeds with timber and old copies of The Daily Telegraph and The New York Times , and keeps feeding through the afternoon.

These days he rarely leaves the house, but his assistant Deborah is proud of the fact that she got him to attend Electric Picnic last year. Visitors do come to Levington, and then he holds court. Johnny Depp came last November with Cillian Murphy, and there's a photograph of the two of them above the fireplace. Depp and Donleavy have been in discussions since 2005 about making a film of The Ginger Man – they first met at the New York Athletic Club, where Donleavy frequently stayed. It hasn't yet come to pass, though Donleavy is confident that it will: "It is under option at the moment." He shows us the visitors' book with Depp's signature. Under address he'd written "unknown".

He is engaging company, sprightly and fit, with a tendency to leap up from his chair and shadow box. He tells me he is wearing his old US navy cap, which he keeps warming on the range. It’s a relic from when he served during the second World War and he makes me feel how heavy and well-made it is. We settle in, and I’m reminded of a quote from Hunter S Thompson: “Reading Mr Donleavy is no longer like being dragged into a beer-brawl in some violent Irish pub, but more like sitting down to an evening of good whiskey and mad laughter in a rare conversation somewhere on the edge of reality.”

Today, he's in full flow, a stream-of-consciousness that flies off in different directions. His old navy cap leads to talk of how he came to Ireland, under the GI Bill of Rights for ex-servicemen, with fees and expenses paid by the US government, enrolling in Trinity College to study bacteriology. The son of Irish emigrants, he had grown up in New York, but on moving to Dublin, quickly took to a bohemian lifestyle, and started writing The Ginger Man .

The novel, which details the drunken exploits of a rowdy young American studying at Dublin's Trinity College after the second World War, certainly has a loyal following. It has reputedly sold over 45 million copies in two dozen languages. While most readers would be hard-pressed to name many of his 23 other books (among them The Beastly Beatitudes of Balthazar B ) , only three have ever been out of print.

Initially entitled Sebastian Dangerfield , the book was initially rejected by 30 publishers, before being bought by Maurice Girodias, then owner of the Olympia Press in Paris, who first published the novel in 1955.

Olympia Press was noted for its mix of both interesting and controversial texts; Watt by Beckett was followed with Lolita by Nabokov. But around the same time, Girodias began to publish a pornographic series called The Traveller's Companion , which The Ginger Man was included in, much to Donleavy's horror, and he subsequently promised that he would "redeem and avenge this work".

He would later be sued by Girodias for breach of contract, but after a legal battle over 20 years, Donleavy ended up owning the very publishing house that had caused him so much anguish, referring to the law as “reassuring rather than romantic”.

The Ginger Man emerged at an interesting period in Irish social and legal history, and was promptly banned, along with books such as Edna O'Brien's The Country Girls , and John McGahern's The Dark , under the eye of Archbishop Charles McQuaid. The ban remained until the 1970s, and it was barred in the US until 1965.

“It was an antagonistic time, because after the war, people were reorganising their lives, although it opened up society somewhat because people were going to pubs, and engaging in new friendships. I was studying bacteriology – a grim business, and I had to go to a lot of autopsies. Dublin was a terrible place at the time. I used to walk through the slums, and in the houses you would see rats running across hallways, with doors torn off. I was shocked to death by what I confronted. It was a very intimidating place.”

The eventual success of The Ginger Man and his second novel, A Singular Man , made him famous, even notorious. Preparing for this article, photographer Brenda Fitzsimons remembers her parents telling her to leave the room during The Late Late Show when Donleavy was about to be interviewed by Gay Byrne.

But the literary world held him at arm's length and awards were not forthcoming (although he did win the 1961 Evening Standard Drama Critic's Award for Fairy Tales of New York , the title later borrowed by The Pogues's Shane McGowan for his hit song) .

Around this time, Donleavy was living the country life in Kilcoole, Co Wicklow, with his first wife, Englishwoman Valerie Heron. They had two children, and Levington Park houses many of his daughter Karen’s ceramics. His son Philip, who now spends time with him at Levington, works in film, though Donleavy points out that at one time he was a professional footballer.

His first marriage broke up in the 1960s, and he went on to marry an American actress Mary Wilson Price. The couple had two children, but it later transpired that neither child was his, his wife having had relationships with two members of the Guinness family, brothers Kieran and Finn. Wilson Price later married Finn Guinness, and talked candidly about her children, Rebecca and Rory, having three fathers. A visitor to Levington in recent years blogged that the author told him that his wife had removed a lot of the furniture.

These days Donleavy spends most of his time in his study surrounded by a vast archive of manuscripts, screenplays and notes, and the first, handwritten draft of The Ginger Man , with notes in pencil by his great friend and drinking partner, Brendan Behan. Behan was the first to champion The Ginger Man , and the first to read it. The story goes that he broke into Donleavy's cottage in Wicklow, where he left unsolicited notes and his signature on the draft manuscript.

Donleavy followed many of his suggestions, and recalls that Behan told him, "Mike, this book is going to beat the Bible." Boxes of correspondence – to figures such as Robert Redford and Jackie Onassis, add up to an archive that he says will one day be bought by a university. Some years ago he told The New York Times that this could be worth $7 to $8 million (€5-€5.8m).

He writes here, every day, in longhand. It is ordered chaos. There's a box marked The Dog on the 17th Floor , a manuscript he has been working on for several years. "The publishers want to publish it, but I am slowing it up. It is hard when you have 25 manuscripts on your mind."

I see a bust of Joyce on his grand piano, and it’s said that the author stayed in Levington Park in 1900 with his father Stanislaus, who did some work on the electoral rolls in Westmeath.

Donleavy regales me with brilliant anecdotes from his past. Richard Harris, who played Sebastian Dangerfield on stage (closed by the “Catholic Authority” after three performances at the Gaiety in 1959), was “charming in every way you can imagine, but he wasn’t someone you wanted to get in a fight with”.

I ask him about the story that he was to fight the writer Norman Mailer, because they both “didn’t like the sound of each other”. He qualifies this: “Yes, I think we were to fight, but we seemed to immediately strike up a friendship.”

Boxing has been a consistent passion of Donleavy’s, and there is a beautiful black and white photograph of him and Joe Frazier next to the kitchen dresser. “Ah yes, he was getting some tips.” Boxing was something he learned early on at school, and continued with when he trained with the legendary Arthur Donovan at the New York Athletic Club. He says that he is possessed of “a tremendously fast left hook, quickly followed by the right”. He shadow boxes every day to keep fit, and at different turns gets up to give me a demonstration.

People used to travel to Dublin to pick a fight with him, from Berlin to New York, “Having a beard seemed to provoke some sort of challenge wherever one went, yet I was peaceful as could be and treated it as a sport. You had to explain to people in Davy Byrne’s that you weren’t doing anything, that you were being challenged because of your beard.”

He doesn’t travel much anymore, and hasn’t been back to New York for a while. When I ask if he feels most at home in Ireland (he became an Irish citizen in 1967), he replies: “Levington Park is the world I know now, I have been here for half a century,” and his identity, though Irish-American, is very rooted in a bohemian Irish tradition.

Levington's crumbling grandeur seems to infuse our conversation, with Donleavy recalling one memory, which then crumbles into the next. We start talking about his new work, which somehow leads to a discussion about the IRA and its relationship with The Ginger Man .

"They would often read it in prison, so they started to follow what I was writing. Prison has been strangely helpful to me, as it has been to a lot of authors, as reading becomes an essential part of prisoners' existence. When I had some trouble on the land years ago, there was a headline in The Irish Times , 'Ginger Man in Land War' – and then suddenly it was quiet. I found out that the IRA went to every single house around here, saying 'do not interfere with JP Donleavy'."

He chuckles at the memory, perhaps because it makes a great story, which is his daily pursuit. I ask him about his fascinating friend Gainor Stephen Crist, who was the inspiration for Dangerfield. He left Ireland for Spain in the late 1950s, but around 1964, he disappeared. Some reports claimed that he simply vanished, while others said that he died in 1979 in Tenerife. There were subsequent sightings in Barcelona, and Donleavy thought he once saw him on Nassau Street, back in Dublin.

“It is a mystery. I think his whole nature was like that though, his interest in the world was like that. Even to this day I wonder where he is. He could be alive somewhere. I went to visit his grave on that island, and being brought to the grave by the cemetery keeper, he was quietly amused, and so I knew Gainor wasn’t buried there, although his name was on the gravestone.”

As dusk settles around Levington, he tells me another story for the road. It is about Brendan Behan, who knew how much esteem Donleavy had for style, and he admits that he was “very cautious” about his clothing and shoes. Behan was staying with him in Wicklow and wanted to go to the pub. “So he took all my shoes in bags and walked over the wet fields, putting on my shoes, and throwing them away as they got wet. When I asked him why, he said: ‘I didn’t want to take a drink in wet feet’.” Donleavy laughs at the memory.

The day draws to a close and his son Philip appears, offering a lift to the railway station. Donleavy wants to talk on, and poses brilliantly for the camera, staying perfectly still for long periods. He’s enjoying the company. “You get so cut off from people, in this house here, and that is not a good thing. My old pals are not around any more, have probably died or something.”

It is fitting that the evening has ended with a story about Behan. What is striking is that the memory of Behan's encouragement seems to linger more deeply in Donleavy's consciousness than the missing shoes, or lack of awards, or domestic strife, and I instantly think of this, from The Ginger Man: "Sometimes I feel 53. Seldom, but at times, I feel 20. Like the days. Ever feel a Saturday on a Tuesday? Or a week of one Friday after another? Recently I've been 70. But I remember 34 as a fine age."