During the general election campaign, the Today programme decided to enliven its coverage by inviting the public to pen poems to mark the occasion. The listeners produced - pretty much as you might have expected - a collection of scabrous, satirical, cynical and witty verse whose main theme was "politicians - a plague on all their houses". But one poem stood out for a humour that was affectionate, rather than biting.

During the general election campaign, the Today programme decided to enliven its coverage by inviting the public to pen poems to mark the occasion. The listeners produced - pretty much as you might have expected - a collection of scabrous, satirical, cynical and witty verse whose main theme was "politicians - a plague on all their houses". But one poem stood out for a humour that was affectionate, rather than biting.

Its subject was the BBC's political editor, Andrew Marr, and in it a female listener gave him her vote because "he floats my boat with those ears like a monkey". Marr covered his embarrassment, characteristically, by speed-writing a poem in response. But is was a striking moment. Not for the first time, the man with the perfect face for radio had become the story.

Over the past five years Andrew Marr has transformed himself from a reporter into a celebrity. Conformation of that came this week when it was announced he was stepping down as the BBC's political editor to take over from Sir David Frost with his own Sunday morning breakfast-time show.

He leaves the corporation's most high-profile and most highly stressed job - to which he brought a bizarre arm-waving style more redolent of a racecourse bookie than a magisterial political analyst - to almost unqualified acclaim. "He has revolutionised political reporting," said one senior BBC executive yesterday, "giving it wit and accessibility without losing any of its authority".

"He is simply the best political editor we've ever had," said one of the biggest household names in British broadcasting, speaking off the record, for fear of upsetting previous holders of the job.

But not just them. There is a powerful minority inside the BBC that is pleased to see Marr go. "He always spread himself too thin, what with his radio and TV chat shows, his journalism and his books. To be a really first-rate political editor you shouldn't have the time for all that." There is another reservation too. "There was just too much showmanship," said another senior executive. "There's a side of Marr that is serious and introspective, but there's a sense that he always used the story to promote himself. There was something very self-indulgent about him. It's always been the Andrew Marr show."

Marr's fans reject this. He is, admirers say, as near as we get nowadays to a Renaissance man: a polymath of politics, painting and poetry, as interested in the sciences - he picked Darwin as his Great British Hero for one recent TV series - as the arts or the political and social sciences. In his comparatively short career (he is still only 45) he has been an acclaimed reporter, an insightful columnist, an eccentric editor and authoritative and amusing political analyst.

Andrew Marr was born in Glasgow. After studying English at Cambridge, he joined The Scotsman. He was a member of the political team at the launch of The Independent in 1986 before returning to The Scotsman as political editor and then moving, in what he has described as his Thatcherite period, to The Economist as political editor. He then returned to this newspaper as chief political commentator before being made editor in 1996, a position from which he was sacked in 1998 after refusing to implement yet another round of cuts to the editorial budget.

It was not the high point of his career, as he disclosed recently. He was asked: "What qualities does a newspaper editor need and how many of these do you think you had?" Marr replied: "An editor needs: reasonable courage, sticking power, imagination, diplomacy, amazing stamina, ferocious attention to detail, numeracy, chutzpah, moral intelligence (well, not all of them, obviously) and luck. In my case: yes, no, yes, no, no, no, yes, no, yes, no. So, four out of 10: not enough."

Two years later, in 2000, he took over the BBC's top political job. Not everyone was welcoming. "The last thing we need is a failed newspaper editor," one disgruntled BBC executive complained when it was announced that Marr was to take over what is probably the most influential job in British journalism.

The Daily Mail led a campaign against him. Marr was not just known as a left-of-centre columnist who had been one of the most insightful writers on the rise of New Labour because he was so close to it; he was also married into a Labour family - his wife, the political journalist Jackie Ashley, is the daughter of campaigning Labour peer Jack Ashley. The Mail branded him as Tony Blair's poodle.

He is generally regarded to have made the transition at the BBC with adroitness. "It wasn't easy," says one fellow political commentator. "As a columnist he was meant to have views. As the BBC's political editor you're not meant to have any. Andy was very skilled in wooing the Tories to position himself as impartial."

But he displayed other new skills too. Those required of an analyst for the widest BBC audience, in three-minute sets of sound-bites, are very different from the ones Marr had demonstrated in the past. That he made the transition is evidenced by a string of awards: Political Journalist of the Year, Broadcaster of the Year, Creative Media Journalist of the Year and Best Individual Contributor on Television.

He is not without his critics. Not all his political judgements have been accurate. "He's made a number of wrong calls," said a BBC insider. "Gordon Brown's speech at the Labour Party conference, which had a coded attack on Blair in virtually every sentence, was said by Andy to be 'an outbreak of unity'. He got two major resignations wrong, saying that neither Mandelson nor Blunkett would have to resign, not long before each did. And he under-reported the degree of discontent with Iain Duncan Smith as Tory leader, probably because he was over-sensitive to the accusation that he was pro-Labour."

But most regard this as nit-picking. "He has got it right most of the time, by a long chalk," said a senior figure inside the BBC's News and Current Affairs department. "And he has made it all so interesting and accessible. Some people might say that there have been too many gags, but better that than too few. He has been a breath of fresh air amid all the BBC lifers."

One of Marr's most engaging characteristics in all this has been his lack of cynicism. Critics might say that he has given the Government the benefit of the doubt a few times too often, but Marr extends that natural charity wider than to one party. He was incensed on the Today programme one morning, during the recent election campaign, after a long barrage of withering cynicism against the political class in general. "There are fools and liars in politics, as in the rest of life, but there are decent, fairly frank politicians aplenty," he has said. Cynicism, he believes, is one of the greatest banes of contemporary culture.

It is responses like that which explain perhaps why Marr is as well liked among politicians as among listeners and viewers. That, and his boyish charm and sense of humour, which seem to have increased over the past five years, even as he has brought his wild gesticulating and his fondness for extravagant and tortured metaphors under control. It may be, too, that this famous talker has started to listen a little more, a skill he will certainly need to practise when he takes over David Frost's seat.

There has been, for Andrew Marr, a cost to all this success. Whether or not he has stretched himself too thin in all this work, there is no doubt that he has stretched himself over the past five years. In addition to a job which most people would regard as more than full-time he has hosted Radio 4's literati salon Start the Week, had his own political/cultural chatshow for contemporary thinkers on BBC4, and done various political documentaries for BBC2, Channel 4 and Panorama. He has even appeared in Doctor Who.

All this is in addition to painting. (He paints and draws as well and as quickly as he writes, landscapes and portraits in oil and watercolour which he describes as "poor imitations of people I admire, from Marquet to Paul Nash, and really not much good".) And reading poetry, for which he has a particular fondness, not least because he can read it on tubes and buses when we lesser mortals merely stare out of the window. And then there is running - he does 19 miles, three times a week, in Richmond Park not far from his home in Putney. It wears me out just thinking about it.

The upside of giving up his day job is that he may now see more of his three children. Marr has a son, aged 16, and two daughters, 14 and 10. His biography on the BBC website jocularly lists "remembering his children's names" as one of his hobbies. But it was striking that, in answering readers' questions in this newspaper just last month, Marr, who gave florid or flippant responses to most questions, gave just a one-word reply to one inquiry. Asked: "Is it possible to be a successful journalist and a successful father?" he replied simply: "No."

"The hardest thing in my life is not being around at homework time," he once told me. "But journalists are market traders going round selling our barrow of thoughts or experiences. We're terrified people might stop buying. So you say yes, while your face fits."

Andrew Marr's face certainly fits just at the moment- even the most curmudgeonly of his critics could not deny that. The question is: will he now use that to take a little more control of his life? Or will increasing celebrity just sweep him to ever more frenetic levels of activity?

A Life in Brief

BORN 1959 in Glasgow.

FAMILY Married Jackie Ashley in 1987. One son, aged 16, two daughters 14 and 10.

EDUCATION Craigflower prep school and Loretto school, Edinburgh. BA in English from Trinity Hall, Cambridge.

CAREER 1981-86: The Scotsman; 1986: joined The Independent at its launch as political correspondent; 1988: The Scotsman political editor; 1989: political editor of The Economist; 1992-96: chief political commentator, The Independent; 1996-98: editor, The Independent; 1998-2000: columnist, Daily Express and The Observer; 2000-05 BBC political editor. Awards include the Richard Dimbleby Award at the Bafta Television Awards in 2004.

HE SAYS "I'm not ultra-ambitious. I don't want to earn lots of money or have a fancy title. But I do loathe boredom."

THEY SAY "Hello, I'm your son." - the words with which Marr's eldest child introduces himself to his father