The 40-year-old actor and wife, Fergie of the Black Eyed Peas, welcomed their first child, Axl Jack, on Aug. 29.
"What's surprised me the most is how well behaved he is. I was expecting a crying baby all the time and he's been a really mild-mannered," Duhamel said.
But he's aware of what could be in store if the couple ever decides to expand the brood.
"I think somehow biology, the universe, whatever, you know gives you like a pleasant baby first so that you have another one, procreate, and then the next one's a holy terror and then you really realize what being a new parent is all about," joked Duhamel Thursday at the opening-night gala for the Wallis Annenberg Center for the Performing Arts.
Fatherhood may have brought some life changes for the "Transformers" star, but he said his approach to his career remains the same.
"No I'm not going to let that affect the way I make decisions creatively," he said of becoming a family man. "I still want to push myself and do things that I would never, that I would never thought that I was able to do."
Duhamel arrived to the star-studded soiree feeling good and surprisingly well-rested for a new parent.
"Well we're both sleeping a little bit less, but you know he's worth it," he said. "Man he's definitely worth it."