But Dempsey (45) had never acted in a big-budget action picture - and the long wait landed him a doozy of a spectacle.
In director Michael Bay's Transformers: Dark of the Moon, he plays Dylan, a wealthy car collector and entrepreneur who figures into the plot in a surprising way and allows the actor to exercise some acting muscles he had never before used.
"There was one reason to do Transformers: to show that I can do this kind of movie," Dempsey said recently from Los Angeles.
"I had met Michael at a Ferrari event a year ago, and we got to talking about cars and that I race, and he told me about this character in the movie who did the same thing. There were a lot of really wonderful things that clicked into place. I read the script and really liked it, and I thought it would be fun to do something like this.
"It's unexpected, coming from me. I need to show people I can do different things than the things I've been doing up to this point."
What about Bay's reputation for being a demanding director who punishes his actors?"
In one of the first meetings we had, he said, 'Look, I want you there on the set first thing in the morning. You won't be going back and forth to your trailer. I'm ready to work 12 hours straight, nonstop.'
"And he's there, on the set, ready to go from the moment he gets out of his car, and he expects you to be there right behind him. As long as you do that, you have a really good time.
"He has an amazing attention for detail, and the sheer size of this movie is just incredible. The amount of focus and attention it takes to get everything working, and the amount of different teams he has to keep organised - he's a really good leader, and he's very passionate about what he does."
