In My Way, his personal anthem, Frank Sinatra sings: "I've lived a live that's full." The same could be said of Pete Hamill, the Irish-American author and journalist, who jokes that he recently celebrated what the comedian Jack Benny called "the 30th anniversary of my 39th birthday". And he's still going strong, writes Deaglán de Bréadún

We're sitting in a bar, but Hamill is drinking Diet Coke. Some journalists are famous or, rather, notorious for their drinking, but Hamill is famous for giving up the drink and then writing eloquently about it in his 1994 memoir, A Drinking Life. It's the story of how he trailed his father into saloons as a boy and came to the conclusion that "part of being a man was to drink". As an adult he justified his drinking because he was still able to function and get his work done. But at 37 he began to notice tell-tale signs of deterioration. He would misspell simple words maybe eight or nine times in a row, and his fingers sometimes felt "like gloves filled with water". At a New Year's Eve party with his girlfriend, the film star Shirley MacLaine, he noticed his hand trembling as he lit a cigarette. Later that night he decided: never again. That was in 1972, and he hasn't touched a drop since.

But in his drinking days a favourite watering hole was P. J. Clarke's, a traditional-style saloon and restaurant in Manhattan. In Michael Mann's film The Insider, from 1997, Hamill appears in a cameo role, meeting Al Pacino at P. J. Clarke's to discuss a scandal in the tobacco industry. In real life he used to meet Frank Sinatra when the Chairman of the Board happened to be in town.

He has written about these encounters in a fascinating little book called Why Sinatra Matters, but I wanted to hear the stories first hand. Hamill was never part of the notorious Rat Pack that clung to the singer through the years. "I was a kind of New York friend; I was never in his house in California." His portrait of Ol' Blue Eyes differs from the traditional media image. "I liked him a lot, because among the things that are not generally associated with him was that he was very intelligent. He wasn't well educated, but what the hell? Neither was I in any formal way. I think he liked that. He didn't have to sit across the table from a guy with a degree. He really had thought about a lot of things. One of the reasons was that he was an insomniac, so he would be up late, reading most of the time."

Sinatra was only beginning his political journey to the right at that stage. "It's like Reagan in a way. They were passionate Democrats, both of them, but the Sixties pissed them off. I remember writing a column one time about this and saying that the famous generation gap of the time was between the people who remembered the Depression and the people who had no experience of it at all." As for 1960s music, Sinatra "could see the Beatles, but he couldn't get the Rolling Stones".

The singer never showed Hamill his darker side, the foul temper and roughneck behaviour. "He knew I was a newspaperman; he must have known that some of what he was \ was going to be recorded somewhere. So who knows if he was on best behaviour, or what?"

So why is Sinatra still important? "Because I think the music is still some of the most vital music ever made in the United States. In pop music, in technical terms, he was the first guy to create an urban sound. If you listen to that music you know this is someone from a city. This is not country and western, as much as I love Hank Williams and Webb Pierce and people like that. And it's not the real blues: it's an urban, ethnic kind of blues. It's got a blues intention, but it doesn't sound like 'the blues'. And it's not like Bing Crosby, which was a kind of area-code-800 music. . . . He was good, but he wasn't from anywhere. You knew this guy came from the immigrants of the East Coast: that's where it came from."

Hamill has his own theory about Sinatra's Mafia associations. "I would go to these concerts and shows and everything, and the wise guys would show up. I think they were fans more than anything else." The singer even wanted Hamill to write the Sinatra autobiography. "I thought about it and I said: 'Frank, I'd have to talk to you about a number of things that might make you uncomfortable: the music, the women and the wise guys.' And he said: 'Music, I can talk from now till dawn. The women, I loved them all. But if I talk about some of those other guys, someone might come knocking at my f***ing door.' "

Later Sinatra came back to him, to say: "Look, from the Thirties on I worked in clubs and in Las Vegas. I didn't meet any Nobel prizewinners there." But Hamill points out that they had no influence on the music: the entertainer wasn't thinking of the Mafia when he sang his love songs, he was thinking of his latest heart-throb. "Ava Gardner shaped the music more than any gangster ever did."

The Sinatra volume, slim but stylish, like its subject, recently came out in paperback, and Hamill has published 17 other books. Nine are novels, the latest of which is Forever, a historical saga about an Irishman who in 1740 sails to New York, where he acquires a mystical gift that enables him to live for ever - as long as he remains on the island of Manhattan. The story takes us through the history of New York, up to and including the September 11th disasters.

And there's no sign of him putting down his pen. "I just finished a book called Downtown, which will be out the end of October, I think, which is non-fiction. [It's\] an idiosyncratic view of New York, so that Rockefeller Center, which is on 53rd Street, is uptown, but P. J. Clarke's, on 55th Street, is downtown - in my view of the world - because it's got that patina of the 19th century."

Clearly, one of the reasons Hamill was drawn to Sinatra was their common immigrant heritage, one of them Italian, the other Irish. Both Hamill parents came from Belfast, although they met in New York. "My father, William, was born on the Lower Falls. My mother, Anne Devlin, [came from\] the Short Strand." His father left in 1923, aged 20; his mother emigrated in 1929, aged almost 19. "They sold the piano to pay for the ticket." Billy Hamill was an enthusiastic and talented member of an Irish soccer team called, his son thinks, The Wanderers, who used to play other immigrant teams in New York. "They played a German team and a Spanish team; there was a Jewish team called House of David."

But tragedy struck. "In 1927 he gets kicked in a game - a double compound fracture in his left leg. They take him off to the public hospital called King's County, there's no doctors around, and by the morning gangrene had set in, and they amputated, so he lost his leg." He was only 24. His father had an artificial leg fitted and carried on undaunted. Some years later he met Anne at a social event for Irish immigrants in Manhattan. "He had already lost a leg when he met my mother - at a dance."

Times were hard, and there were few luxuries and little cash to spare in the Hamill family household in Brooklyn. For his parents there was also the memory of past privations. "Working itself, for the Catholics of that period who had been shaped by Belfast - just having a job - was a triumph. They never thought about having a career or anything like that; that was for their kids." Pete left school early and ended up in the navy. After a spell at art school in Mexico he returned to New York as a designer on a magazine for Greek immigrants, published in their own language, which Hamill did not speak. He tried his hand writing a piece for the magazine in English, about a Hispanic boxer, a friend of his called Jose Torres, who later took the world light-heavyweight title. The owner was nonplussed and demanded to know, in halting but memorable terms, "why eez, in a Greek magazine, a story about a Puerto Rican fighter, written by an Irish guy, in English?"

Hamill eventually moved on to a job on the New York Post, and his career in journalism began to take off. A city newspaper strike in the early 1960s gave him the opportunity and incentive to go to Europe, and he spent 16 months in Dublin and Barcelona, writing for the prestigious and now sadly defunct Saturday Evening Post magazine (which had no connection with the New York Post). "It was a great, dopey job: I interviewed Brigitte Bardot, Sophia Loren, Sean Connery when he was just starting the James Bond movies, Michael Caine . . . "

He was in Belfast the night news of John F. Kennedy's assassination came through and recalls how both sides of the community were equally stricken. "People were weeping on the Shankill Road as badly as they were on the Falls, because I guess they felt, somehow, he was theirs too. He had been in Ireland the previous June, so the television must have had a huge impact at the time." He went back to New York, where the New York Post offered him a regular column in October 1965. "I thought it was going to be one of these nice folksy little local columns, and by Christmas I was in Vietnam. The Sixties had begun." The column appeared four times a week. "But I was young. I couldn't wait to get up in the morning. I think four is easier than one, because \ one a week you try to hit it out of the ballpark. At least if you're doing four, even if you really botch a column, you get up in the morning and do it again. But I was young, I was full of energy, loving the work. You know, to have a job that you love is so hard to get."

This continued until 1974. "I left just before \ Murdoch bought the paper. I went off to just make some money, because I had two kids and I was making no money in the newspaper business." He went back to journalism in 1977, writing for the rival New York Daily News. "Basically, I have been back and forth between the two tabloids ever since."

He attracted attention in Ireland with his columns on the Long Kesh hunger strikes in 1981. "I was sympathetic to getting the thing over with. I hated terrorism then. I hate the idea that you stick a bomb somewhere in Donegall Square and some woman with a baby carriage gets killed. I can't stand that. I felt a lot of pity, too, for the British soldiers: you get some kid from Leeds or somewhere getting plug-ged over something that he has nothing to do with. But I understood what they were driving at, even though I didn't think it was going to have a happy ending."

He felt the pull of his Belfast roots. "They were something I had to struggle against." But he developed an understanding of the Protestant community's viewpoint from reading the poems of John Hewitt. "He helped teach me how to think about it." At this time his columns alternated with those of another prominent Irish-American writer, Jimmy Breslin. "It's not the same as being a reporter, but the authority for the opinion is the reporting. It also keeps you fresh and it keeps you from being an ideologue, because you're constantly getting your ideas disrupted by these people: the guy you think is a miserable, rotten bastard turns out to be OK."

He has also been editor of both the News and the Post - the first for eight months, the second for five weeks - as well as the Mexico City News.

Along the way he found time for such activities as writing the sleeve notes for Bob Dylan's Blood On The Tracks album, in 1975, which earned Hamill a Grammy Award. He also became involved with some of the world's most interesting and glamorous women, such as the late Jacqueline Kennedy. "I have never seen a person whose public image and private reality were so different. The one thing you never get in these endless combinations of books and docudramas and all that is her sense of humour, her wit, her sense of irony about the world. You never get that from anybody. You never get her knowledge of literature, which is why she was a good editor, making books happen when she was at [the publishing company\] Viking. It's a totally different image in a way; part of it was because she didn't co-operate with the publicity machine: she wasn't going to sit on the Today show and talk about her grief over Jack."

He spends most of his time now in Mexico with his second wife, the Japanese journalist and author Fukiko Aoki.

Hamill comes across as a courtly man, pleased to sign my copy of Forever. He is always happy to sign his books, joking that Norman Mailer advised him once: "Sign them all, because they can't send them back!"

Forever: A Novel is published by Little, Brown & Co at £7.99