The actor who plays Pete Campbell in Mad Men reveals why he's quite unlike his odious character – but why it's a joy to play him

Sometimes, Vincent Kartheiser says, fame isn't all it might be. He's sitting telling stories on an old car seat on the porch of a house in West Hollywood in the April sun. For instance, he says, he'd met a woman the previous night and they'd talked for 10 minutes, before she had asked him the inevitable question: "How do I know your face?"

Kartheiser had no option but to own up. "I said, 'I'm that guy Pete Campbell in the TV show Mad Men.'"

And then it started. Kartheiser shrugs, resigned: "She said, 'Oh my God, I fucking hate you.' And I go, 'Well, you mean you hate my character.' She said, 'No, it's more than that. When you come on the screen, I don't want to be in the room. It's a completely physical thing. You make my flesh creep. I loathe you.'" Kartheiser laughs a little wildly. "I mean, where do you go from there?"

If you've seen even a single episode of Mad Men (and if you haven't, you must) you will know exactly what the woman meant and exactly why, off screen, Vincent Kartheiser seems at pains to be everything Pete Campbell is not: scruffy, charming, relaxed, witty, unshaven, likable. Mad Men is set in the world of New York advertising in the 1960s, in a fabled, sharp-suited, scotch-drinking, skirt-chasing, unreconstructed male paradise at the dawn of the consumer age and Pete Campbell is the serpent in its garden, the repressed, preppy malcontent in the offices of Sterling Cooper, forever in the shadow of Don Draper, the square-jawed genius of the sales pitch (played with supreme style by Jon Hamm).

There is a much-trafficked website dedicated to the idea "What would Don Draper do?"; there would never be a website called "What would Pete Campbell do?" Still, Kartheiser is fascinated by – and touchingly loyal to – the weak-willed and neurotic monster he has created. "You know at the end of series two," he says, with some surprise and pride, "Pete sits cradling a gun on his lap [a long story involving his failing marriage and a doomed office affair], well apparently most of the audience was desperate for him to shoot himself."

In person, Kartheiser has none of Campbell's oiliness, but a good deal of his complex compulsion. He's 30, but has been acting for 25 years and even off screen it seems hard for him to stop. He is the youngest son of six; his father was a tools salesman, his mother ran a nursery. "I was," he suggests, "aged nine, the go-to kid in Minneapolis for a commercial voiceover." He is now the go-to guy for a certain kind of smooth and boyish psychosis, Iago dressed by Ralph Lauren. He was, therefore, a natural as the avenging and unhinged film producer Fielding Goodney in the forthcoming BBC adaptation of Martin Amis's 1980s parable Money.

Kartheiser is by far the best thing about a curious two-parter in which Nick Frost (of Shaun of the Dead and Hot Fuzz fame) plays the yobbish antihero John Self and which only haphazardly captures the baroque paranoias of Amis's prose. Against Frost's prosaic English self-destruction, Kartheiser supplies poetic American menace. As in the book, Fielding's eyes are "supercandid cornflower blue", he has a "high droll forehead" and he makes twisted mockery of Self's ambition to make a Hollywood movie and his zeitgeisty obsession with filthy lucre: "Money doesn't mind if we say it's evil, it goes from strength to strength. It's a fiction, an addiction and a tacit conspiracy."

Did Kartheiser know the book when he took the part?

"No," he says, "but of course I read it when I got the offer. I laughed a surprising lot, though it's kind of relentless in its tone.'"

Amis once noted of the character he plays, I point out, that "he embodies confidence which, at least in my novels, is a psychopathic state".

Kartheiser grins his slightly at-one-remove grin: "I definitely do psychopathic," he says. "I don't try to but it just sneaks out of my character. Goodney has an outward sense of confidence but I don't know how deep it goes."

The same sense of fragile confidence seems to be true of Kartheiser. He's clever and manic in the hour or two that we talk, sometimes vulnerable, but never quite in earnest, antic and boyish, shouting occasional funny obscenities at the Observer's photographer, Barry Holmes, and his assistant as they set up.

Directors, I say to him at one point, seem to see a duplicity in him, a useful doubleness. Where does he think that comes from?

He looks askance, or mock askance. "Well, I think certain roles are chosen for us. The moment I read Pete Campbell I thought: I can do this, this is mine. And in Money, too. The truth is I turn down a lot of projects. If a character doesn't have some kind of internal struggle, it's no good for me. I think to live in the unnatural world we live in and not have some kind of unresolved issue going on would be naive in the extreme."

Kartheiser, like his characters, seems to invite psychoanalysis, partly because, you guess, he rarely stops analysing himself. He's given up on therapy, he says, "because though I like generally to be healthy in my life, I sometimes like to be unhealthy in my thoughts and my actions." A Vanity Fair profile recently followed him on to the set of Mad Men where he was, unsurprisingly on the evidence of our interview, the noisiest of presences: "Between shots, Kartheiser pinwheels around the set, teasing the crew and other actors or loudly psyching himself up for the next shot. It's a funny kind of psyching up. 'What's wrong with me! Fuck life in the ass,' he shouts after one take. 'I'm off today – I know it! I know it! Don't bullshit me,' he yells after another. 'I wish I could be anyone on earth but me!' As a colleague says, 'It's kind of unusual, but it works for him. It's what Vincent needs to do to lose his self-consciousness.'"

Does he use those McEnroe-ish techniques for a purpose or do they come naturally?

"The second before you film something," he says, "you want to get in your body. I might scream something to wake up the nerves in my nose and my lips and my eyes, you know. That's where I do my work."

One of the things that Mad Men does – the series is created by Matthew Weiner, also the intelligence behind The Sopranos – is to suggest the admen as archetypes, always selling versions of themselves to anyone who will listen, Gatsby-like, and Kartheiser, on screen, is able to convey that sense of himself perfectly. It is, I guess, also the enduring fate of a child actor – he graduated quickly from schoolboy Shakespeare and "being kind of the perennial Tiny Tim" to movies in which he played opposite Andy Garcia, Christian Slater and Charlton Heston in his teens. In among all the riddling personas, does he have a stable sense of who he is?

He considers for a moment. "I know there is someone in there," he says. "When you are walking home from a bad situation, that person is the voice in your head. It's the person who tells you exactly what you feel and what you trust. It's like when you look at photos of yourself as a kid, or family movies, you immediately see yourself and you know exactly how it felt to be me there. But I guess we are all on a big search to figure out who we are."

Some of the ways that Kartheiser has chosen to do this are unconventional, at least among Hollywood TV stars. He has, for example, in the city of cheap gas and freeways, given up on a car.

"I go on the bus, I walk. A friend left his car recently at my house and I took it out one day just for 15 minutes and it was terrible. You know why? I felt like I was back in LA again. Four or five years ago, when I had a car and I had been out of the city I wouldn't feel I was back until I got in the car, you know. But now I feel off the grid. I feel that I am not part of the culture. And because I don't have a car I don't really go anywhere to buy things. In fact, I have been in a slow process of selling and giving away everything I own."

He has? Like what?

"Like, I don't have a toilet at the moment. My house is just a wooden box. I mean I am planning to get a toilet at some point. But for now I have to go to the neighbours. I threw it all out."

(As he says this, I'm wondering whether this is just another of the parts Kartheiser might be trying on for size, but to prove the point he later takes me back to his house, which really is an empty wooden box, a small one-room bungalow on a nondescript Hollywood street and indeed it has no lavatory.) Is that a Buddhist thing, I wonder, or an early midlife crisis thing?

"It started a couple of years ago," he says. "It was in response to going to these Golden Globe type events and they just give you stuff. You don't want it. You don't use it. And then Mad Men started to become a success on a popular level and people started sending me stuff, just boxes of shit. Gifts for every holiday, clothes. One day, I looked around and thought 'I don't want this stuff, I didn't ask for it'. So I started giving it to friends or charity stores, or if it is still in its box I might sell it for a hundred bucks. I liked it so I didn't stop."

Does he have a bed?

"I do," he concedes, "but that might go…"

A TV?

"Actually, that was the big discussion today, when a friend came over: I was wondering, should I have a screen in my home? It seems like the next step. I haven't had a mirror for six or seven years, though I admit that causes a lot of problems when I have to tie a bow tie. Or if I have to, you know, comb my hair for something. I'm forever looking in the mirrors of parked cars."

It sounds a bit like an extreme reaction to the venal material desire of Mad Men (and Money). He's not worried about this tendency at all?

He laughs. "I probably should be worried. Sometimes, I look around my house and think: is this normal, Vinny? I mean it's a bit more than just a remodel…"

So what does he do with all his money?

"I don't have a lot of money. I get some from Mad Men. But I don't think I'm rich…"

Surely he should be by now? Mad Men sells across the world. Or is his agent very rich?

"I don't really use an agent," he says (though he is signed to ICM). "Maybe that's where I am going wrong. TV is very different from where it was 10 years ago. There are so many more channels, so much less ad money; contracts have gone through the floor you know, at least mine have.

"Someone is no doubt making a ton of money. It's like all creative media; you know there's definitely money in it somewhere, but it doesn't go to the actors or the writers or the journalists or whoever; we are way, way down the food chain."

As if to prove this point, he tells me how the previous weekend he had gone in search of a rock in Topanga Canyon north of where he lives. The rock was to make a basin in the gap where his bathroom once was.

"I picked out one rock, in the river, like a 650lb rock," he says. "A monster stuck between two other rocks. We were in the river and we got it moving but this guy comes out shouting, 'You can't take my rock!' I'm like, 'It's the world's rock!' And anyhow I needed it for my sink… but in the end we left that rock alone and we had to find another rock. We got a cool one."

Is he aiming for a caveman kind of look?

"No, I'm going for a Japanese industrial feel."

Not very woman-friendly, I'd say.

"I guess not."

In Mad Men, Pete Campbell seems stuck in an endlessly deferred coming-of-age tale. Though he has the wife and the apartment and the executive job, he doubts that he is a man, at least not a man like his bullying father, or a man like Don Draper. In describing the series, Matthew Weiner has said: "We'd all like to be Don but actually we are all Pete." Does Kartheiser, single, possessionless, doing brilliant make-believe for a living, have anxieties in this regard by any chance? I ask.

"I don't think anyone feels like a grown-up," he says. "I have four sisters and they all dated guys and they are all married, and all of the guys they dated always seemed to me like grown-ups, you know, but eventually you come to see that underneath they are all little boys really. Grown-up is just a word that kids use to describe someone who is not having any fun."

In his slightly androgynous anxieties about masculinity, Kartheiser suggests, Campbell is much more "contemporary" in his sensibility than the impervious Draper. "I see grown men screaming at televisions in bars, or playing golf, or whatever. We all fear that we are going to be found out as a fraud. I bet, I don't know, Stephen Hawking sits there hoping no one is going to see through his disguise."

The great strength of intimately observed period pieces such as Mad Men, and Money is that they hold a mirror up to our own times. What lessons does he take from it?

"Mad Men is about that whole idea of corporate money as we understand it and how it was really built by America. We are seeing the fallout of some of that now."

Though Weiner is in overall charge of the nuance of the story, nearly all his writing team are women. Does Kartheiser think that is one reason that men – vain, unfaithful, treacherous – don't come out of it too well?

"Well, men are assholes at some level, aren't they?" he suggests, with feeling. "The powerful white male in history is like the most evil entity, isn't he? Mad Men is a portrait of white men doing their stuff, just as their power is coming under a bit of threat. Don Draper is from a time when he can persuade everyone that what he is doing is right. Pete can't quite do that. He fears his shallowness. But don't we all?"

Kartheiser hints at a suitably complicated private life. "I've never been monogamous," he says, at one point. "It might happen, but it never has yet. I don't understand women, I'm off that kick." He wears a wedding ring, "just so I can flash it to warn people off if I need to," he laughs, in a stagey demonic way, "or at least put it on in the morning."

Does he fear that fame will get in the way of any relationship or, at least, Pete will?

"I'm just not that grounded. I just think LA is a very tough place in that respect. Since Mad Men got popular, I spend more time with my family. I like going back there."

Not surprisingly, given the epic nuance of his characterisation – he likes to refer to Mad Men as "a 700-page novel" – he confesses to having been obsessed with Russian literature between the ages of about 13 and 17. "I was a nut for Dostoevsky. You can tell a lot from what people read between those ages. My brother was a Steinbeck freak and now he lives in a little village in New Hampshire and he's a baker."

They see each other often. Does he sometimes envy the comparative simplicity of his brother's life? "Constantly," he says, "but my brother knows me better than I know myself; I've always been jumping on one stage or another."

One of Pete Campbell's most memorable lines was the plaintive: "Why can't good things happen all at once?" He is plagued by the thought that any success is always tinged with the knowledge of past failure and of failure to come. It sounds like that strikes a note with Kartheiser, too.

"Well," he says, after briefly suggesting that he cries most days, "the great thing about my life is that I have this other family waiting for me, too, on the set of the show. Mad Men is the single greatest working experience of my life. And I imagine I may well always think of it like that. Even when I am not working I go in just to watch, you know."

He can't wait, when we speak, to get into series four, five months of intensive work (and fewer worries about bathrooms). It's therapeutic, he suggests, to the extent that every time he steps into Pete Campbell's rather tight-fighting shoes he finds out what Vincent Kartheiser is made of: "Your cue comes, and you step up to your mark, and each time you have to discover whether you can still really do it."

Unlike his alter ego, Kartheiser could sell you any idea, but on this particular pitch I'm not quite convinced. Even when, for a photograph, he stands in an empty swimming pool, with a noose around his neck, he never for a moment forgets who he is: a natural-born actor and one who never stops auditioning for the fleeting, engaging role of himself.

Money is showing on BBC Two in May as part of the channel's 80s season