Today, the man who has materialized inside a Manhattan hotel suite to talk about his new film, “Mud,” has been radically transformed from his former party-boy days. After flaunting his chiseled body in hot pants and a half shirt in 2012’s “Magic Mike,” the actor underwent a dramatic physical change last year — shedding more than 45 pounds — to portray Ron Woodroof, an AIDS-stricken, drug treatment crusader in the forthcoming drama “Dallas Buyers Club,” due out in the fall. Gone are the once-sprawling set of pecs, cascading locks, and facial scruff that helped land him the title of People magazine’s Sexiest Man Alive in 2005.

McConaughey, who has gained back some of the weight, still cuts a handsome figure, but he sports a slimmer build and a leaner, clean-shaven mug. Yet his dreamy Texas drawl and unfussy introspection remain, as does his easygoing bonhomie and the thousand-watt smile that could charm the habit off a Benedictine nun.

McConaughey’s physical transformation also reflects the onscreen reinvention that he’s been busy crafting over the past several years. He was once best known for his breakthrough role as skirt-chasing stoner Wooderson in the cult classic “Dazed and Confused,” and for dramas like “A Time to Kill,” “Lone Star,” “Contact,” and “We Are Marshall,” But the 43-year-old actor had become mired in empty-calorie rom-coms — “How to Lose a Guy in 10 Days,” “Failure to Launch,” “Ghosts of Girlfriends Past” — playing his signature role of the roguish yet charming womanizer.

Then, last year, McConaughey began popping up in intriguing little indie gems like “Bernie,” “Killer Joe,” and “The Paperboy,” in parts ranging from a scarily sadistic cop with a fried chicken fetish to a closeted journalist with a dangerous yen for S&M. He even tweaked his own beefcake persona, creating a fully fleshed portrait of a sleazy-yet-seductive male strip club impresario in “Magic Mike,” a performance that earned him a best supporting actor award from the New York Film Critics Circle.

His latest film, “Mud,” finds McConaughey as a heartsick fugitive-drifter hiding out on an island in the Mississippi River, inside an old power boat that somehow came to rest high in the branches of a tree. When his title character is discovered by two teenage boys, he befriends them and enlists their help to reunite with the love of his life, Juniper (Reese Witherspoon), and to elude capture by some very bad men.

“The McConaissance,” as one glossy magazine dubbed his reinvention, even extends to his formerly free-spirited personal life. The actor, who’d once been arrested in Austin after cops found him at home loudly banging on his bongos in the buff, is now the married father of three children, all under the age of 5. There’s little time these days for impromptu road trips in his Airstream trailer or surfing sessions with buddies like Kelly Slater.

Of the career shift, McConaughey says it wasn’t about wanting to shed certain perceptions that the public had of him or fears of Hollywood pigeonholing. It was simply a desire to challenge himself as an actor.

“I was still receiving scripts that I liked. But it was stuff that I felt like I could do tomorrow or next week. There were some action films. There were some romantic comedies. But then I felt like, ‘You know what? I’m starting a family. I’m going to be a dad and hang around and get a homestead going. So I’m going to wait for something else to come my way,’” says McConaughey, in town on a short break from filming a new HBO series, “True Detective,” in New Orleans with his buddy Woody Harrelson.

“I was looking for something that was going to move the floor a little bit. Shake me. Scare me a little bit. Make me go, ‘Whoa! I don’t know what I’ll do with that role, but it’s turned me on. I’m attracted to it. Let’s go do it and find out.’ . . . And what happened is, because I said ‘no’ to some things that I probably would have taken before, all of a sudden, cyclically, these other things came back to me, and I started getting calls from [directors] Billy Friedkin, Steven Soderbergh, and Lee Daniels about these roles.”