"We didn't take a broad enough view of our responsibility, and that was a big mistake. It was my mistake, and I'm sorry," Mark Zuckerberg confessed in his written testimony published by a House of Representatives panel.
"I started Facebook, I run it, and I'm responsible for what happens here," the businessman added.
Twitter users have been vividly debating Zuckerberg's remark.
Zuckerberg is giving testimony to the US Congress on Tuesday.
Facebook's data leak scandal broke out in March when it was made public that personal information of about 50 million Facebook users had been harvested by the Cambridge Analytica consultancy firm without their permission.
While working for major political campaigns, the firm gathered data to develop a mechanism that would predict and influence the behavior of US voters.
Earlier in the week, Facebook estimated the number of users affected at around 87 million, mostly located in the United States.