He is set to appear before a joint hearing of the Senate Judiciary and Commerce committees on Tuesday afternoon followed by a House Energy and Commerce Committee hearing on Wednesday morning. Facebook's share price has dropped almost 15 per cent since news of Cambridge Analytica came to light in mid-March.
Facebook disclosed in September that Russians under fake names had used the social network to try to influence United States voters in the months before and after the 2016 election, writing about inflammatory subjects, setting up events and buying ads.
After resisting previous calls to testify, Zuckerberg agreed to come to Capitol Hill this month after reports surfaced - and the company confirmed - that Cambridge Analytica had gathered Facebook users' data.
"We didn't take a broad enough view of what our responsibility is, and that was a huge mistake", Zuckerberg said during a press call.
It took Facebook until September 2017, 10 months after the election, to go public with its first findings on the Russian meddling, which it says appeared in the news feeds of 126 million customers - equal to almost half the adult population of the United States. It was the tail end of a Facebook era defined by connected apps: games like FarmVille, Candy Crush and Words With Friends; apps that broadcast your extra-Facebook activities, like Spotify and Pinterest; and apps that were nearly explicitly about gathering as much useful data as possible from users, like TripAdvisor's Cities I've Visited app, which let you share a digital pushpin map with your friends.
The hearings were scheduled to address Facebook's use and protection of user data in the wake of the Cambridge Analytica scandal. In Monday's prepared testimony, he summarized investments the company is making to prevent fake accounts and monitoring activity around elections.
Zuckerberg's testimony said the company was "too slow to spot and respond to Russian interference, and we're working hard to get better". The Facebook CEO is in the nation's capitol Monday morning for meetings ahead of the testimony.More news: If US wants a trade war, China is ready to fight
More news: WaPo: Trump not now a target of Mueller criminal probe
More news: Villanova sets Final Four 3-point record, crushes Kansas 95-79
We asked Facebook Australia about the notification, and while it didn't have any specific details about when the affected Australians would be notified, the company did say it could be as early as today.
Users who were not affected will see a different link highlighting which apps are connected to their Facebook accounts and what data those third parties can see. Given that business model, how much can Facebook really limit access to all that information?
He's expected to concede that Facebook "didn't do enough" to prevent a host of problems on its platform, such as fake news, foreign interference in elections, hate speech and data privacy.
But a larger body of research suggests that Facebook, as well as other social media, tend to reinforce and intensify existing political views by creating an echo chamber of friends and like-minded users. He said recently the company will make its "controls and settings the same everywhere, not just in Europe", although it wasn't clear exactly what he meant, nor how that would affect data collection and privacy.
On Monday, he was pictured in one photo showing his mobile device to Senator Bill Nelson, the top Democrat on the Senate Commerce Committee.
But he did not explain why and how Cambridge Analytica still managed to misuse the personal data afterwards.
CONTEXT: Sean Parker, Facebook's first president, said Facebook specializes in "exploiting" human psychology and may be harming our children's brains.