Hundreds of fans showed up to see Psy speak, but the Korean rapper was still stunned to be there, Billboard reported.
Harvard professor Carter Eckert, who organized the event, said he planned the discussion to look at Psy as a "modern global digital phenomenon."
Psy said it was "so weird" to be speaking at Harvard, or any Ivy League school, for that matter. He joked that his academic performance led him to be known as WWF, which he says stood for withdrawal, withdrawal, failure.
"The class was too early," he said.
Psy attended Boston University for four years to study management.
He joked that he has heard rumors that he's the first to give a speech at Harvard without a script.
The music video for "Gangnam Style" went viral -- it became the most-viewed video on YouTube with more than 1.5 billion views -- and even that was a surprise. His new single "Gentleman" has more than 300 million views.
"Gangnam... was an accident. And accidents don't happen often," he said in the speech.
Psy said he doesn't plan to replicate its success -- partly, he said, because it's difficult to get there. And partly because he is fully overwhelmed by his rise to fame.