Deep in the heart of Texas the stars are famously big and bright, but celestial watchers may have noticed them dimming recently.

Fear of competition with Matthew McConaughey, perhaps. The actor, father, and son of Texas is "having a moment" the way Archie Gemmill had a moment against the Netherlands in the 1978 World Cup.

Having juked his way past a reputation as a bare-chested stud muffin in romantic comedies, McConaughey has had a run of box office and critical hits. Now in possession of both a Golden Globe and a Screen Actors Guild award for his latest film, Dallas Buyers Club, the 44-year-old is in contention for the best actor Oscar on March 2. It is one of the toughest fields in years, with Christian Bale (American Hustle), Leonardo DiCaprio (The Wolf Of Wall Street), Chiwetel Ejiofor (12 Years A Slave) and Bruce Dern (Nebraska) also in the running, but who would bet the oil rights against McConaughey?

Our meeting in London starts in true Gemmill fashion with a spectacular kick. When I enter the room there's the usual dance over who wants to sit where, and in the process I hoof a bottle of water that's on the floor. "That's all right," says McConaughey in his molasses drawl, "we'll get a cloth." Less than a minute in the company of the man People magazine once dubbed "the sexiest man alive" and already he is doing the housework. If there had been a small animal in need of rescuing the father of three would probably have done that too. (He has form in that area, saving stranded pets after Hurricane Katrina.)

McConaughey is a gentleman. But as his progression from rom-com star to Oscar contender indicates, he is not interested in finishing last. While he resists the notion that he had some grand plan, only conceding that he made a few "conscious decisions" to change direction, there is something more to the tale. Behind the story of the successful but undervalued actor who went from Fool's Gold to box office gold lies another.

Before we turn those pages, there's another fine yarn in Dallas Buyers Club. Directed by Jean-Marc Vallee, it is the true story of Ron Woodroof, an electrician and good ol' boy who liked to party hearty. Told in 1985 that he was HIV positive, doctors gave Woodroof 30 days to live. What happened next was an astonishing illustration of one man's rage against the dying of the light and medical bureaucracy. While the authorities were dragging their heels, Woodroof started an international search for affordable remedies, bringing medication back to America and selling it through his club. In making a buck he prolonged his own life and that of others.

McConaughey liked that Woodroof was as much a hustler as a hero yet it was a heartfelt story. "I thought what a great way to tackle an Aids drama, from this guy's point of view. It didn't have the sentiment that this subject usually has. Not to say it doesn't have as much meaning. I think it has more meaning because it is not a 'message movie'."

The script had been in development limbo for 20 years. It was only when McConaughey said yes that it began to have a chance of being made. Even then, it was a struggle. But turning in outstanding performances in films from The Lincoln Lawyer to Bernie (directed by Richard Linklater), Killer Joe (William Friedkin), Mud (Jeff Nichols), Magic Mike (Steven Soderbergh) and The Wolf Of Wall Street (Martin Scorsese) gives an actor a chance to turn red lights to green.

Rewind to the early noughties and the thought of McConaughey working with Scorsese might have been the basis for a Saturday Night Live skit. So used were audiences to seeing McConaughey bare-chested it might have been hard to recognise him with his shirt on. Matt Damon had a running joke with late-night TV host David Letterman in which the Bourne star would impersonate McConaughey and somehow work in a line about taking his shirt off. In another measure of how times have changed, Damon spoke recently of working on Christopher Nolan's hugely anticipated science fiction film Interstellar, out in November, in which McConaughey is the lead. "Talk about being in the zone," said Damon of his co-star. "He's really just crushing everything right now." Nobody is laughing at McConaughey these days.

Well, maybe they are smiling a little. His acceptance speech at the Screen Actors Guild awards, in which he compared the buzz of acting to taking a flight to Neptune ("They'd better have the sprockets rolling when you get off that spaceship!") sparked a few grins. Given the chance to speak about acting, his love of what he does, allied to his natural Texan loquaciousness, can produce all-round-the-ranch responses.

McConaughey is an old-school character actor rather than a modern method man, but for Dallas Buyers Club he lost more than three stones to play the ailing Woodroof. The first week on a strict diet he was grumpy. After that he went into an almost spiritual mode, getting up earlier, reading more, feeling more alive. "There's a freedom in being able to have a singular focus."

He and his wife Camila Alves have two sons and a daughter, ages from two to six. His youngest son is called Livingston, not after the West Lothian town but after several individuals McConaughey met during his travels in Africa, Australia and elsewhere. "I can't wait to hear him say my name is Livingston McConaughey. It has strength to it, it has dignity. It's like a lumberjack conductor," he laughs.

McConaughey was born in Uvalde, Texas (population 16,000) in 1969. His father worked in the pipe supply business and his mother was a teacher. The three McConaughey boys had Huck Finn childhoods. "The rule in our house was: if it's daylight you are outside." He swears by the outdoorsy life, so much so that he and his wife set up a non-profit foundation called Just Keep Livin, which offers fitness and confidence boosting programmes to high school students.

His childhood sounds like perfect preparation for Mud, in which McConaughey played a drifter washed up on an island in the Mississippi. "That was a real adolescent trip for me, that character." Does he still regard himself as an adolescent? "No, I think of myself as more of a man. But being a father definitely makes me younger in certain ways." Kids make you look at things afresh, he says.

The couple's first son was born around the time McConaughey's career began to change. Career-wise, he says, there was no epiphany, no conversion on some road to a thespian Damascus. Before the rom-coms, indeed, his career had been pretty toasty. His first major movie was Linklater's cool Dazed And Confused. This was followed by John Sayles's acclaimed crime drama Lone Star, the John Grisham thriller A Time To Kill, then Steven Spielberg's Amistad and Robert Zemeckis's Contact (with Jodie Foster). McConaughey was getting the meatier parts, but just not enough of them.

The rom-com decade, from The Wedding Planner to Failure To Launch followed. Critics threw words such as "agonising", "nauseating" and "smug" like confetti. McConaughey wasn't feeling any pain. "I was enjoying my career. It had been good to me, I was doing my best to be good at it." But he was curious to know what else might be out there. He wanted to feel daunted. So he started saying no to the rom-coms.

"I was conscious that this probably meant things were going to dry up for a while. I talked to my wife about it, my agent. Made that decision. Had to say no to these things for six months. After that six months, a year passed when I got nothing. Nothing came."

For someone who grows anxious when he's not working, it was not easy. But something good came from that plunge into anonymity. "All of a sudden I get a call from Steven Soderbergh, William Friedkin, Mud comes up, Bernie. These things came up. I didn't chase them."

So what made the difference? It could have been starting a family, entering his forties, the alignment of the moon and stars, or luck. Perhaps it just came down to timing. The younger McConaughey had a good rep with directors but he was arguably too good looking for the parts they wanted to fill. But time, so often the enemy of actors, was on his side. When he "reappeared" as Mickey Haller in The Lincoln Lawyer he was all of 42, but in one sense he was born again.

It wasn't just time. On Dallas Buyers Club, Vallee recalls McConaughey's script being covered in notes. "I've rarely seen an actor work like he has and prepare like he did." I had read that he switched from law to film at university after reading The Greatest Salesman In The World by Og Mandino. Published in 1968, the self-help book cum fable tells of a wealthy merchant passing on the secrets of his success. Its teachings are simple but seductive: "I will greet each day with love in my heart"; "I will persist until I succeed", and so on.

Reading the book, it seemed that McConaughey had done more than just pick it up while at university. So it proves. He has gone through many copies. "Two of them I've had to put in Ziplocs and put away in a treasure chest because they became so frayed. One got eaten by a friend of mine's dog. I had to go round picking up hundreds of pieces and tape them back together. A couple of other ones I have written in so much that I've had to get new ones."

Why does he need a self-help book? "I've always liked philosophy. I'm always trying to improve as a man. I love trying to figure life out. Part of that is I've got to know myself." And part of that is to stop apologising for the rom-coms. Or at least he's trying to. When I ask if it bothers him to have those brought up he says it's the nature of the game. "Do I want to change people's perception of that? No. I don't feel like spending any time on that." But then he does just that. "Not all of them are good," he says. "Some of them are really just lazy rehashes of certain things. It's a genre I did well in and it did well for me for. It sure as heck paid my bills. Even to this day. They were fun. I call them Saturday afternoon characters." The characters he's been playing recently are very different. "They're Tuesday morning characters. Wake up - we've got some responsibility here."

Dallas, his character in Magic Mike, Soderbergh's tale of a troupe of male strippers, was certainly not Saturday afternoon watch with mother material. He had to strip in front of a female audience that was not backward in coming forward. Scary? "Hell yeah, it was scary! That was a great buzz though. Hoo-eee!" It was never written in the script that Dallas dances but Soderbergh said it would be a good idea. "I'm like, 'No way, no way,' then a voice on the other shoulder said: 'Are you kidding me?'"

Dance he did, and proceedings duly got a little wild. Almost going Full Monty was not in the script either but someone in the crowd had not read that page. "I came out in a G-string and I was down there and some girl reached over and ripped it, it broke. I felt this cool breeze coming so I made my move, held on to it, rolled out of it, stood up and walked off. But it was coming off!"

He coped with it better than most actors. "That's how we grew up, we're a hugging and kissing family. Physical intimacy is not something we back away from."

I'm reminded of the time 15 years ago when he was arrested for disturbing the peace. When the police arrived, he was naked and playing the bongos. You don't do that any more then?

"You said I don't," he replies.

Well, do you?

"I've got like 35 different drums from all over the world that I've gathered, and yes, I still play them."

In the nude?

He gives that big skies smile. "Possibly."

Good to see he's taken to heart Mandino's "I will laugh at the world" teaching. But McConaughey does not have to convince anyone of his seriousness any more. n

Dallas Buyers Club (15) is in cinemas now