TORONTO – Quebec director Jean-Marc Vallee says Matthew McConaughey was “on a mission” to reinvent his career with his much-lauded turn as renegade AIDS patient Ron Woodroof in “The Dallas Buyers Club.”

“It’s a giant performance,” Vallee said at the recent Toronto International Film Festival, where the movie screened. “When we were on the set I was forgetting to say ‘cut’ sometimes … I was so moved.”

Critics have been similarly dazzled by McConaughey’s portrayal of Woodroof, a real-life heterosexual electrician (and part-time rodeo rider) who contracted HIV and — unhappy with the treatment from his doctor — began smuggling unapproved drugs from Mexico, both to take himself and to sell to others.

The “A Time to Kill” actor is practically unrecognizable in the role and much has been made of his shocking weight loss, but McConaughey says it was reading Woodroof’s diary that ultimately provided the key to the character.

“You know, there’s who we are and there’s who we portray ourselves to be,” the actor said at the festival, still looking thin but no longer emaciated.

“Boy, the ‘who he was’ that I got from his diary really helped me grab (on) to say, ‘OK, I have ownership of the man.’”

The film, which co-stars Jennifer Garner as a sympathetic doctor and Jared Leto as a drag queen who goes into business with Woodroof, paints a vivid portrait of the early days of AIDS, when the medical community knew little about how to treat the new scourge.

“He was figuring it out like everyone else,” McConaughey said of the hard-living Woodroof, who battled the FDA for the right to choose his own medication and died in 1992.

“Here’s a guy with a seventh grade education…. He hadn’t really found his way or a purpose in life, you know, (he) was going to get away with what he could. And really, the guy got purpose when he got HIV and the purpose was: ‘What am I going to do to stay alive?’”

Garner notes that “a terrible complacency has set in” when it comes to HIV and hopes the movie pushes the issue back into the public conversation.

Despite that wish, “The Dallas Buyers Club” never feels preachy.

Indeed, McConaughey says he and Vallee were united in their view that Woodroof should retain his essence as a “hell-raising bigot” and that he not have a “coming-to-God moment in act three.”

“I kept saying if we keep him human, the humanity will come out,” said McConaughey. “He’s not the guy who’s going to grab the white flag.”

McConaughey has made a conscious decision in recent years to take on edgier roles in films such as “Magic Mike” and “Killer Joe” and it’s clear he forged a strong creative connection with Vallee, noting he was impressed by the director’s Genie-winning “C.R.A.Z.Y.”

“I try to grow (with) each of my roles and I feel like I’ve been doing that more so in the last few years…. I had an incredible experience doing this,” he said at the festival.

Garner, too, said she was energized by Vallee’s guerilla style of movie-making. “Dallas Buyers Club” was filmed in 27 days on a shoe-string and Vallee says the first cheque only arrived a day or two before the shoot began in Louisiana (a location that was chosen because of the tax breaks).

“I kept saying, ‘keep the faith guys, (the money is) coming, this film is written in the stars…. It’s happening, we’re doing it. We have to believe in it because we’re here and it’s too late to go back.’”

Vallee’s technique was a totally new way of working for Garner.

“I never, ever in my life made a movie like this,” said the “Alias” star, lauding the “little Montreal crew” that shot the film and marvelling at the use of natural light and handheld camera work by Quebec cinematographer Yves Bélanger.

“(The camera) was always on Yves’ shoulder,” she said. “It was incredible. If there was a steady shot it was because he didn’t sneeze during it. It was 100 per cent on Yves.”

She added: “We didn’t stop and rehearse, we shot the first rehearsal and we went with it…. They would say ‘Cut!’ and they’d say: ‘OK, what’s the next scene?’ … It was really, really invigorating and exciting.”

For McConaughey, preparation was key. He spent about five months losing the weight (Leto is also alarmingly thin in the film).

Garner admits she was concerned about her near-skeletal co-stars noting that Leto seemed wobbly at times.

“Of course I was concerned,” she said. “It’s one thing to see them with the ‘remove’ of a screen. To see them in real-life, evolution in your brain tells you ‘feed that person, that person is ill, that person is not going to make it.’

“I was more than concerned. I hated it.”

Vallee, however, said he trusted the pre-shoot work done by McConaughey, who seems certain to receive an Oscar nomination for his performance.

“He’s a big boy, he’s a professional,” said Vallee. “Matthew was such a force, he was the engine.”

He added: “This guy was on a mission to change the perception, to change his life, change his career. He was waiting for this kind of material … and now he had the (chance) to go out there and do it and he went and he did it all the way.”

“Dallas Buyers Club” opens Friday in limited release.