I wouldn’t be caught dead wearing this,” says Michael Stipe in mid-stride, as he hurries through Chinatown. He’s actually quite fetching, in wraparound shades, tight corduroy trousers and a V-neck T-shirt with a safety pin, but his point is not so much about the clothes as about their suitability for a gentleman of his years. He was caught in a downpour earlier in the day, so his own carefully chosen outfit, now soaked, is rolled up in a plastic bag swinging at his side while he wears borrowed clothes.

Stipe has been the front man of REM for 27 years, and they’re still going strong, days away from making their 14th album. He is so enthusiastic and energetic on this stormy, monsoon-like day, as we navigate downtown New York, I have to ask him to slow down. But then, Stipe never stands still. Something of a renaissance man, he has produced films – including Being John Malkovich and Velvet Goldmine – published a photography collection, used his fame for social and political causes and been a mentor to talents as varied as Thom Yorke and Courtney Love, and now, at 47, he’s a shirtless model for Marc Jacobs. “I don’t ever want to repeat myself,” he says. “I’d rather fall on my face publicly with a really bad song than crank out something mediocre or vaguely reminiscent of Losing My Religion or Everybody Hurts. F*** that. Great songs – already did it. Let’s move on.”

Last night, he was at the Marc Jacobs fashion show. He came with Heath Ledger and was sitting with Vincent Gallo and Juergen Teller, the photographer.

Shooting Stipe for the ad campaign is a clever piece of casting. When REM’s first album, Murmur, came out in 1983, the band more or less invented alternative rock, as well as the fashion that went with it, thrift-store chic – which is, of course, what Jacobs does best, in a high-fashion kind of way.

Stipe stops in his tracks and turns around to stare at a pigeon, telling me that, when the weather is weird, he takes his cues from wildlife. He keeps walking fast, occasionally checking his BlackBerry, until we have gone through Chinatown and into SoHo, where he stops at a framing shop to ask a smoking proprietor about the paintings in the window. He lights his own cigarette before setting off again, then says: “Smoking and walking, gross,” but does it anyway.

Finally, we arrive at a cafe, where he buys me a mango lassi. His wallet is a plastic envelope torn in half, which contains his keys, a digital camera, money and tobacco. He says he tells people that it’s a new accessory. I say the fashion-model thing must be getting to him, and he laughs. In the campaign, he’s shirtless, in a pair of electric-blue corduroy trousers, looking annoyingly slim. “How about that? In my own bathroom!”

Stipe once said: “Critics hate me because I have a six-pack”, and when I remind him of that, he laughs out loud again. “It’s more like an eight-pack now. Did I really say that? That’s pretty good. The thing I dislike is when people are mean-spirited. I just think there’s enough shit in the universe. And snarkiness and vulgarity. Maybe I’m a pretentious f***, but I want to elevate. I want to raise. I want to be inspired. I want to live in a place that feels inspiring to me.”

Later next month, the band are planning on recording in London, where they love the artistic energy and have done ever since they played the Marquee back in 1983. There, they will wrap up that next album. “I can’t wait,” he enthuses. They’ve taken a new approach, doing live rehearsals in Dublin over the summer. “We had tickets so people could come and watch us rehearse. It was really nice to play stuff that nobody’s ever heard, and in some cases the songs were only half-written. Then we could go straight into the studio with that material – it’s very effective.”

Age, it seems, cannot wither the band. A few years ago, Stipe took some flak for comparing himself to Brad Pitt and Tom Cruise, neither of whom is vilified for doing what he does, at more or less the same age. “The point is about ageing with grace,” he says. “My gripe was simply a comparison: why, in that medium [film], are they exonerated from the same criticism that I’m getting in my medium [music]?”

I mention that I saw Sean Penn a few days earlier, who is exactly the same age as Stipe. Between the two of them, being a 47-year-old smoker never looked more glamorous. “He has all his hair,” says Stipe. “I feel there’s a grace in accepting one’s age and being okay with it, and not trying to be something you’re not. I find that vulgar.”

It should be pointed out that Stipe shaved his head about a decade before everyone else did. “Douglas Coupland once said, if you want to be remembered a hundred years from now, create a hairstyle. It was after River [Phoenix, Stipe’s friend] died [in 1993]. Public figures were not doing that at the time – they were pretending they had hair.”

It happens to be Tuesday September 11, and we’re in downtown Manhattan. I mention Stipe’s quote of three years ago, when he spoke of “the great quiet” after 9/11 and “the period of great personal activism” that followed it. He has been constantly active with benefits and charities, especially in his home town of Athens, Georgia, and, more recently, in the rebuilding of New Orleans. At a certain point, with people such as Stipe, and Penn for that matter, you have to recognise that they mean it – they couldn’t keep it up quite this long just for the publicity. They are the committed ones.

“I think I can speak for Sean, and certainly for my band and myself, when I say there is a commitment behind the action that’s not attached to wanting a headline or having your photograph taken. I think injustice is the one thing that is more of an irritant to me than anything,” he says quietly and earnestly.

Earlier, at the Style photo shoot, Stipe had asked that the INXS song Not Enough Time be played, over and over again, until everyone in the room was swaying to Michael Hutchence’s hopeful lyrics.

Is that what makes you the angriest, injustice? “Yes, I’m the angriest pacifist in the world.”