In the prologue to his recent memoir, Hitch-22, Christopher Hitchens confessed to "customary reservations" about the whole project perhaps being "too soon", but then said that such concerns were swiftly dissipated by the "blunt realisation" that "the project could become, at any moment, ruled out of the question as having been undertaken 'too late'".

These words acquired a new resonance when Hitchens announced on 30 June that he was to undergo treatment for oesophageal cancer. In a short statement published on the website of Vanity Fair, where he has been a columnist since 1992, he wrote: "I have been advised by my physician that I must undergo a course of chemotherapy on my oesophagus. This advice seems persuasive to me."

Hitchens's announcement ended speculation over the abrupt cancellation of his book tour for "personal reasons". The decision to postpone all commitments indefinitely was an unusual move for a writer who, despite his prodigious appetite for booze and fags and his prolific output - regular columns for Vanity Fair, Slate and the Atlantic, 11 books and four collections of essays - prides himself on never missing an engagement.

I recently met Hitchens at a central London hotel to discuss his life and work. It was late afternoon and he was drinking red wine. Because of the publication of his memoir, his tone was largely retrospective, but he also discussed his future plans - a new book on the Ten Commandments and a campaign to have the Pope arrested for the concealment of child abuse. He did not sound like someone preparing to ease himself into retirement.

“One of the great questions of philosophy," he said of his new book project, "is: do we innately have morality, or do we get it from celestial dictation? A study of the Ten Commandments is a very good way of getting into and resolving that issue."

Of his hostility to and pursuit of Joseph Ratzinger, he remarked indignantly: "It's outrageous that people like myself, Richard Dawkins and Geoffrey Robertson are taking this on. What do we have law officers for? What do we have police departments for? But we will do it if they won't."

Christopher Hitchens was born in Portsmouth in 1949, into what he has described as a "family of Tories who had nothing to be Tory about". His father, Eric, a lifelong naval officer known affectionately as "the Commander", met his mother, Yvonne, during the Second World War. Asked what first attracted him to the left, Hitchens cited not an early encounter with Das Kapital, but rather the contradictions and ironies he witnessed at home and at school. (Hitchens was privately educated after his mother told his father: "If there is going to be an upper class in this country, then Christopher is going to be in it.")

“The lesson of my upbringing was that the conservative values of both my family and my school were a bit of a joke because the people who espoused them were also being ripped off by the Conservatives," he told me. "The boys I was at school with didn't know they were lucky; they just took it for granted. This had a very radicalising effect on me."

Hitchens's mother, a gregarious and affectionate woman, was ultimately bored by his austere father and eloped with Timothy Bryan, a defrocked priest who had become a devotee of the Maharishi Mahesh Yogi.

In 1973, at the age of 24, Hitchens suffered what he describes as a "lacerating, howling moment in my life", after learning that his mother had been found dead in an Athens hotel room in what was initially treated as a murder, but turned out to have been a suicide pact between Yvonne and her lover. By this time, having graduated from Oxford in 1970, Hitchens had become a staff writer at the New Statesman ("all I'd ever wanted to be"); he filed a long piece on the military coup that provided a backdrop to his lonely trip to Athens to reclaim her body.

A divided self

Anthony Howard, New Statesman editor from 1972-78, recruited Hitchens as part of a celebrated generation that included James Fenton, Martin Amis and Julian Barnes. He remembers him as a talented writer - "Hitch could produce a front-page leader, which would take me a couple of hours, in half an hour"- if not a great one. "To me, James Fenton was a much more interesting figure. Fenton was a genuine poet; he had much more body to him than Hitch."

The young Hitch was a big drinker, even then. "He always came in at 10.45am, holding, with shaking hands, this cardboard cup of tomato soup to nurse his hangover."

Howard says he did not anticipate Hitchens's political trajectory but adds: "I was always puzzled about the contrast between his lifestyle and his political views. He was always much more comfortable with people on the right."

Hitchens makes much of this divided self in his memoir. There was Chris, hawking Socialist Worker on street corners and getting duffed up on picket lines; and there was Christopher, who would slip into a dinner jacket and enjoy the high life at All Souls College. One senses that, like Oscar Wilde, who contended that the problem with socialism "is that it takes up too many spare evenings", Hitchens was never comfortable in the world of the subcommittee and the composite motion.

I asked him what he would have done had he not become a writer and, in what sounded like an attempt at self-mythologisation, he said: "[I would have] been someone else, because [writing] is all I ever wanted to do. It's what I am, rather than what I do." However, he conceded that he regretted not entering politics. “I did want to run for parliament. Tavistock Labour Party could have had me if it wanted. I could never quite imagine myself winning, but I'm very sad I never fought a campaign."

By the end of the 1970s, he had tired of Britain ("Weimar without the sex" is his verdict on the Callaghan era) and longed for the bigger stage of the United States. His decision to cross the Atlantic in 1981 was a masterstroke, providing him with a range of outlets - the Nation, Harper's and the New York Review of Books - for the literary-political essays at which he excels.

Moving first to New York and then to Washington, DC, he became known as an aggressive left-winger, stridently attacking targets such as Ronald Reagan, Henry Kissinger and Jerry Falwell's Moral Majority. Hitchens's polemical assaults on Reagan's "sado-monetarism", which once led Conrad Black to threaten to buy up every title he wrote for, remain among his finest.

In a culture where consensus and bipartisanship were viewed as unqualified goods, Hitchens stood out as a contrarian (a term that he perhaps unsurprisingly rejects) prepared to challenge the orthodoxies of both left and right.

Following George Orwell's maxim that "saints should always be judged guilty until they are proved innocent", Hitchens outraged the Catholic right in 1995 with a scathing attack on Mother Teresa over her religious fundamentalism and her support for the dictatorial Duvalier family in Haiti.

This book, The Missionary Position: Mother Teresa in Theory and Practice, was what made Johann Hari, columnist on the Independent and former New Statesman staffer, want to become a journalist. "I read that when I was 14 after I'd seen the documentary on Channel 4, and I just thought it was the most amazing book," he said. "Just taking something that seemed to be taken for granted - that this woman was a saintly, benign humanitarian - and exposing it as a complete lie."

It was after an attack on another revered figure, Bill Clinton, that Hitchens reached the conclusion that personality matters more than policy. "Clinton could change his mind on any issue, but couldn't change the fact that he was a scumbag," he says now.

Today, his criticisms of political figures are entirely post-ideological. I asked him for his opinion of David Cameron, hoping for a robust critique, but he replied: "He seems content-free to me. Never had a job, except in PR, and it shows. People ask, 'What do you think of him?' and my answer is: 'He doesn't make me think.'" The younger Hitchens might have had something to say about Cameron's sinister European alliance or his austerity economics.

Similarly, Sarah Palin is impugned not for her hard-right politics, but for her opportunism. "I think she's a completely straightforward cynic and opportunist and I think she's cashing out," he said. "She's made a fortune and she'll make another. But she's not actually going to do the hard work of trying to lead or build a movement." From the other direction, he praises Barack Obama not for his landmark health-care reform, but for his "clean" presidency and his books. "I voted for Obama positively because I thought the revelation of his character in his books was admirable."

Hitchens's fervent support for the "war on terror" and the invasion of Iraq alienated many comrades, but then his relationship with the left has long been an ambivalent one. He supported the Falklands war, for instance, on the grounds that Argentina's fascist junta had to be deposed. It was over US intervention in Bosnia, not Iraq, that he first parted ways with allies such as Noam Chomsky and Edward Said. On abortion, he outraged American liberals by arguing for the moral and scientific validity of the term "unborn child".

Marxist, but no socialist

Hitchens stopped describing himself as a socialist in 2002, but insists that he remains a Marxist and a believer in the materialist conception of history. This distinction may not be as implausible as it appears. As the political fallout from the financial crisis demonstrated, while Marxism retains immense analytical appeal, it is of little prescriptive value. In Hitchens's boisterous advocacy of the disastrous Iraq war, there is more than an echo of the Marxist belief in the necessity of violence for progress - that nothing should stand in the way of the ­locomotive of history. To the charge that he has embraced neoconservatism, he said: "I'm not a conservative of any kind. A faction willing to take the risks of making war on the ossified status quo in the Middle East can be described as many things, but not as conservative."

And as if auditioning for a role as a latter-day David Hume, he said that his only allegiance was "to scepticism and to doubt", having rejected the view that there is any "universal solution".

“I had plans for the next decade of my life," Hitchens recently remarked to a friend, as if he feared the next decade would not happen, at least for him. "I think, perhaps, I should cancel them." Asked why he quit smoking two years ago (he relapsed while writing the final chapters of Hitch-22), Hitchens said: "Fear. I had smoked enough in my life. The rational part of my brain kicked in and said: 'You must do something.'" Around this time, his second wife, the American Carol Blue, whom he married in 1991, told the Washington Post: "He wants to live - live to see his political enemies defeated." Hitchens, who is fond of quipping that we are "born into a losing struggle", will need all his powers of wit and fortitude as he fights cancer.

“The one unforgivable sin," Yvonne Hitchens used to say, "is to be boring." Whatever else one may conclude, life would certainly be a lot more boring without her son.

Read more by and about Christopher Hitchens

George Eaton writes for the New Statesman blog The Staggers.