After launching Facebook as a sophomore from his dorm room in early 2004, Zuckerberg dropped out later that year to move to California in order to develop the social networking site.
"Mom, I always told you I'd come back and get my degree," he wrote on his Facebook account, which was liked by 1.7 million people by 0130 GMT on Friday.
Facebook has close to two billion monthly active users, and a market capitalization of $450 billion -- the fifth most valuable company after Apple, Google's parent Alphabet, Microsoft and Amazon.
At age 33, Zuckerberg is the youngest billionaire in the world, and the fifth richest person with an estimated fortune of $65 billion.
Bill Gates, the world's richest person, also dropped out of Harvard in 1975, shortly after he founded Microsoft. He received an honorary degree from the university in 2007.