Zuckerberg is scheduled to appear before the Senate Judiciary and Senate Commerce Committees tomorrow, and the House Energy and Commerce Committee the day after.
The Senate hearing, the first of two appearances Zuckerberg will make before Congress this week, begins at 2:15 p.m. ET on Capitol Hill. "We didn't take a broad enough view of our responsibility, and that was a big mistake", he says in the remarks.
Zuckerberg, who has never testified in a congressional hearing, said in written testimony on Monday that he had made mistakes and had held too narrow a view of the social network's role in society. Facebook says most of the affected users (more than 70 million) are in the US, though there are over a million each in the Philippines, Indonesia and the United Kingdom.
The prepared remarks do not reveal new information about how data was shared or what Facebook will do.
"The only thing I really share is recipes, if they want to hack me for my recipes go for it", said Facebook user Mary Beth Vanderbilt.
Some 40 senators out of the 100-member Senate sit on the two committees holding Tuesday's hearing, setting up a possibly marathon hearing.
Zuckerberg also addresses the 2016 election, explaining the website's efforts to block "traditional threats" like hacking and malware, and the company's failure to identify or prevent disinformation campaigns and the coordinated use of fake accounts.
After meeting with Zuckerberg on Monday, Senator Bill Nelson told reporters that he appears to be taking the matter seriously.
Trafficking investigators say they have seen no drop off in the illegal products offered for sale on Facebook after prior public pledges by the company to crack down.
"I've directed our teams to invest so much in security - on top of the other investments we're making - that it will significantly impact our profitability going forward", Zuckerberg said in the prepared testimony. "(Facebook) happens to be the point of the spear, but all these other app sites that get your personal data, that's another way of us losing our privacy".
Moreover, Facebook banned Aleksandr Kogan, a Cambridge University researcher who leaked the data to Cambridge Analytica, from using Facebook data in 2015 and certified that "they had deleted all improperly acquired data", according to Zuckerberg.
"I think he understands that regulation could be right around the corner", he said.
Facebook Canada said notifications would start rolling out Monday, so it could be some time before people see the alert on their news feed.
Around 87 million Facebook users around the world, including 300,000 in Australia, will from today find out if their private data was shared without their permission.
Republican Senator John Kennedy of Louisiana said he wanted candor from Facebook.