Some of us owe Matthew McConaughey an apology. For a substantial part of his career, the indecently handsome Texan had to endure being the punchline to an unstoppable series of unkind jokes. The ruthless people at Family Guy even dreamt up a mumbling, six-packed parody of our Matthew. To many, he was a drawling, blandly attractive rom-com drone in the style of those 1950s actors who lived chiselled lives as Chuck, Chip, Bart and Skip. If you wanted somebody to lean woodenly against Kate Hudson in your poster, then Matthew was your only man.

Then, a year or two ago, something odd happened. The first whiff of revival came with McConaughey's smart performance in the thriller The Lincoln Lawyer. What's this? He was terrific as a slick hit man in William Friedkin's Killer Joe. He was equally good in Steven Soderbergh's Magic Mike and Jeff Nichols's Mud. That leisurely southern charm was stretching itself into some surprisingly ironic shapes. They're calling it the McConaissance. Now, playing a stubborn Aids patient who refuses to die quietly in the fine Dallas Buyers Club, the 44-year-old finds himself odds-on favourite for a best-actor Oscar.

Would it be rude to ask what happened?

“There is a story,” he says. “The thing is, it’s not as clean a narrative as people say. That narrative is a bit ‘then and now’: then I was doing C-plus work; now I’m doing A-plus work. It’s not quite like that. I was doing romantic comedies and action. I enjoyed that. But I consciously wanted to redirect myself.”

My goodness, this man radiates confidence. Dressed in a good grey suit, his hair damply crinkled, he spreads his legs dramatically as if waiting for the arrival of a horse to the resulting gap. This is how we used to think of Americans in the olden days. They were that bit more confident than us. They were endlessly talkative. And they knew how to get stuff done. Just observe how Matt set about recalibrating his career.

“I thought: ‘you know what, I am going to take some time off. I will say no to the things I have been saying yes to. I have a pay cheque. I can pay the rent if I take time off.’ I told my wife it’s going to get dry. I told my agent it was going to get dry for a while. And it got dry for a year and a half.”

I am surprised. I half-thought he would deny that any sort of shift in status had taken place. Oh, I treat all work the same. Oh, I have just been doing what I always do. That sort of guff. But it is clear that McConaughey had a strategy. The chaps who built the Brooklyn Bridge and laid the Transcontinental Railroad also had strategies.

"There was six months of saying no, and then nothing came in for a year," he says. "Then suddenly I became a few smart directors' 'great new idea'. There was William Friedkin on Killer Joe. There was Steven Soderbergh's Magic Mike. But I didn't go chasing that. I sat and waited. There wasn't any rebranding. It was an unbranding. People then thought: 'I haven't seen McConaughey for a while. He might be interesting in this.'"

A cynic might argue that this is just the sort of story that appeals to Oscar voters. A guy gets written off as prime beefcake and then allows himself to evolve into a more Texan Paul Newman. But McConaughey would be a worthy winner for Dallas Buyers Club.

Jean-Marc Vallée's film tells the mostly true story of a singular young tearaway named Ron Woodroof. In the mid-1980s, the jobbing electrician was diagnosed with HIV and given a month to live. At this stage, the authorities had approved few retro-viral drugs and the only hope was to be put on a trial for experimental treatment such as AZT.

Woodroof, a heterosexual playboy who had no time for gay people, began importing treatments from abroad and, exploiting a loop in the law, distributing the medicine via a private “buyers club”. Woodroof survived another seven years and helped a great many other patients extend their lives.

“I didn’t try and imitate Ron Woodroof, even though I had video of him and transcripts,” McConaughey says. “I tried to emulate what he was about. He didn’t ride bulls, for instance. But we fictionalised that and used that as a bookend. Here’s a guy given 30 days to live. He’s got only a seventh-grade education and he educates himself to be an expert. That guy is in there.”

It hardly needs to be said that, in the film, Ron ends up softening and warming to the gay people who share his predicament. His association with a transgender woman – played by fellow Oscar nominee Jared Leto – proves particularly educative. Of course, as happens during every awards season, rumours have begun circulating about the story's accuracy. (Similar chatter has been gathering around 12 Years a Slave and American Hustle.) Last week, a story magically emerged claiming that the real Woodroof was bisexual and may have contracted the disease from a man.

“Yeah, that happens,” McConaughey says in his tolerant way. “There’s a month-and-a-half to go to Oscars. Let’s see if we can poke holes in the legitimacy. I know he was heterosexual from sources who wouldn’t have any reason to lie. I understood he got it through intravenous drug use. I don’t know. But it was interesting that it was told from a heterosexual point of view, because that allowed us to investigate that bigotry and denial early on.”

Clearly serious about his work, McConaughey lost more than 30lbs to play the ailing Ron. When you consider how lean he was to begin with, the achievement is all the more remarkable.

“I went to the nutritionist and it seems that there wasn’t that much of a medical risk if you did it properly,” he says. “I ate two portions of fish a day. I ate two portions of vegetables a day. I had some pudding and eggs in the morning. I ate all that. I just ate small amounts. I gave myself four months and lost three and a half pounds a week.”

So, did he celebrate with a fatty blowout when it was all over?

“Oh yeah! Oh yeah! I had a cheeseburger the day after,” he says. “I waited until 2pm. I made sure I was real hungry. I took two hours to make it and an hour-and-a-half to eat it.”

McConaughey is not exactly as you might expect. He is endlessly charming, hugely polite and better looking than any man has a right to be. But, unlike so many of his characters, he doesn’t speak in any sort of sleepy drawl. Energised and enthusiastic, he leaps his feet during anecdotes and leans in when being conspiratorial.

Where did it all come from? There’s no theatre in his blood. Mom was a teacher. Dad was a gas-station owner and oil-pipe supplier. One doesn’t imagine he was being dragged to auditions as a kid.

“I had no idea I was going to do this,” he says. “We really weren’t media kids. I think I had seen two movies before I was 17. I remember mom saying: ‘You are not watching that TV. Why watch somebody do something when you can get out and do it yourself?’ That’s a pretty good acting lesson. Go be the subject.

“We were great storytellers. We were great bullshitters. We’d sit there every night and tell stories. I am still in the storytelling business. I went and studied film, but I couldn’t let myself dream about being an actor. It seemed impossible.”

His appearance in Richard Linklater's Dazed and Confused (1993) persuaded him otherwise. McConaughey leaps up to act out his singular audition for the film's most dazed and most confused character: committed stoner David Wooderson. He arrived neatly primped in his best suit and then, when Linklater looked unconvinced, allowed his body to collapse into a post-THC slump.

“Suddenly, I am going to work and having a good time,” he says. “I’m getting $320 every day. People are saying: ‘Hey man, you’re good at this.’ Can I do it again tomorrow? In three weeks, I’d made more than I’d made waiting at this blues bar all year. That was so much fun. I thought: ‘I’m going to give this a shot’.”

Things could hardly have worked out better. He came to LA with a plan to support himself as a production assistant. But he got a part at his first audition and never had to consider taking a second job. There are worse things than being typecast as the ambulatory abdomen in yellow-pack romantic comedies. He did his duty opposite Jennifer Lopez in The Wedding Planner. He stood tall before Kate Hudson in How to Lose a Guy in 10 Days and Fool's Gold. He ran up against Jennifer Garner in Ghosts of Girlfriends Past.

Along the way, he met and fell for Brazilian model Camila Alves. They married in 2012 and live in Texas with their three children. The couple now find themselves under a new, freshly terrifying form of scrutiny: the awards- season gauntlet. It's a strange business. When McConaughey made his acceptance speech at the Golden Globes – where he won best actor in a drama – the trade papers treated it as an "audition" for the equivalent Oscar oration. It's a campaign all right and, whether he likes it or not, McConaughey's at the front line with rifle and bayonet.

“Yeah I noticed that,” he laughs. “I didn’t know it was an ‘audition’ until I read about it. I’m not feeling any pressure. Look, if a studio is pushing a film, they want to know, ‘are you going to be a horse in the race?’. Absolutely! I would regret it if I decided not to engage.”

Along the way, he can take revenge on all those of us who once made fun of him. Rub our noses in it, Matt. You’ve got the last laugh.

“No, no. I learnt long ago that none of that is personal,” he says with characteristic decency. “I’m not overly concerned with how I was branded. Hey, bash all those rom-coms if you like. They put food on the table for my three kids. Heck, I may do another.”

He allows himself a moment to savour the glow.

“But, hey, I am really enjoying what I am doing now.”

So are we, old man. So are we.