Having found fame as Derek "McDreamy" Shepherd in hit television show "Grey's Anatomy," Dempsey has been living his dream racing Porsches around the world.
In June, he finished second in his class at the 2015 edition of the grueling Le Mans 24-hour endurance race, and he now plans to produce a television series about the dramas of the racetrack.
"I like this world very much," Dempsey tells CNN inside the relaxed confines of his motorhome at the iconic Spa-Francorchamps circuit where he had competed as a celebrity driver in the Porsche Supercup at the Belgium Grand Prix.
"My desire and passion for racing has always been there and now I'm getting the opportunity to commit to it and to have a strategy to develop as a driver. It's really enjoyable."
Dempsey is competing in his first full season in the World Endurance Championships, a major global series run by motorsport's governing body the FIA.
Hollywood heroes Tom Cruise, Al Pacino and James Garner might have acted in racing films but Dempsey is at full throttle behind the wheel for real.
As the 49-year-old talks motors and movies, his blue eyes flicker with intensity. He has discovered that the racetrack provides an intensity of feeling that is much harder to quantify in his acting career.
"When you're in the car, it's a different physical and emotional experience that I just don't get," he explains. "It's immediate, the results are tangible.
"Success in Hollywood, what is that? What does that mean? Does it mean making money? Does it mean box office success? Does it mean being on a hit show?
"There are plenty of films that don't do well that I would consider successful but weren't considered successful in a business sense. This is tangible, everything else is very abstract."
Born and raised in Maine, the American actor first experienced the thrill of speed through a childhood love of skiing, but it wasn't until the Continental Tire Sportscar Series in 2007 that he had his first major motorsport run.
Now he's raced at Le Mans four times and partnered with Porsche in 2013. All of this after a successful acting career spanning 30 years.
Dempsey is not the first Hollywood star to find the allure of the asphalt equal to the trinkets and thrills of show business.
Academy Award winner Paul Newman and nominee Steve McQueen were both very serious actors and very serious racers. Does Dempsey view himself as a modern-day McQueen?
"A lot of people compare you because you're in the same business but I don't look at it that way," Dempsey considers.
"Steve McQueen was definitely passionate, as well as Paul Newman, but I don't wake up and think that."
Dempsey believes the qualities you need to be a successful actor have helped him in his racing career.
"Good acting is when someone is present," he explains. "Really great actors are in the moment, reacting to what's happening in front of them and you're moved by that. That is very similar to if you're having a dialogue with the car.
"Newman or McQueen -- both really talented in front of the camera and really talented behind the wheel -- understood that ability to stay focused and to be present.
"The beauty of racing is that it really forces you to be present, you don't think about the past or the future. You're just in the minute of that moment, in that corner.
"That's what's really intoxicating about motorsport. The purity of thought."
McQueen's starring role in the 1968 classic "Bullitt" is credited with making car chases cool, but the actor wanted to go one step further and translate motor racing to the big screen just as it was.
The late actor's passion project "Le Mans" -- which was partly filmed during the actual race in 1970 and featured real racing drivers -- was complicated by troubles on and off the set.
"He just wanted to capture what racing was about," Dempsey said of McQueen. "He didn't want to get into something that was too melodramatic."
That conundrum is now facing Dempsey as he begins work on a TV series based on Michael Cannell's book "The Limit: Life and Death on the 1961 Grand Prix Circuit."
The plot focuses on the career of the first American Formula One world champion Phil Hill, who won the coveted title in 1961.
"We know what the story's going to be about and it's now about fine-tuning the history and the racing elements," reveals Dempsey. "It will be a series for cable with the Sundance Channel.
"The frustration is how to communicate to the writers and film makers that racing point of view. If you don't capture that then you lose your audience who love motorsport completely.
"It's a solitary thing when you're in the car. You're alone, you're in a cocoon in many ways and you're out there by yourself.
"There's only one person you can answer to and you know the truth. How do you tell that story, how do you capture that on film?"
For now, Dempsey is continuing to search for answers to other questions on track.
Admitting he might always be "playing catch-up" with the professional drivers he so admires, Dempsey wants to flex his racing muscles for as long as he can.
So far, in this season's World Endurance Cup for GT drivers he has finished sixth at Silverstone and fifth in Spa before a career-high second at Le Mans, along with co-drivers American Patrick Long and German Marco Seefried in a Porsche 911.
"I'm doing this because I love it," smiles Dempsey. "I'm passionate about it but to realize that goal... there was a lot of expectation and desire and when we achieved it, we were all moved by it.
"It made a big impact on me emotionally, and it was an important memory that I'll never forget."
Some of the heart-throb's fans are still struggling to forget his character's shocking exit from the 11th season of "Grey's Anatomy", earlier this year.
But Dempsey the actor, racing driver and father-of-three is now embracing new horizons.
"Hopefully I can keep establishing myself as an actor and as a driver," the 49-year-old, who reportedly earned $16 million in 2014,
muses. "It's about consistency and continuity to both.
"I'm not 17 so I'm going to try and get as much racing as I can at this age and to try to be competitive, to follow my dream as long as I can.
"To be competitive as a driver... to be racing or to win, to be competitive, it's exhilarating.
"What I'm learning here I take back to being a better father... and a better person. It forces you to really look at yourself in new ways. I like that."