John Tye, the founder of Whistleblower Aid, a legal nonprofit that represents people seeking to expose potential lawbreaking, was contacted this spring through a mutual connection by a woman who claimed to have worked at Facebook.

The woman told Mr. Tye and his team something intriguing: She had access to tens of thousands of pages of internal documents from the world’s largest social network. In a series of calls, she asked for legal protection and a path to releasing the confidential information. Mr. Tye, who said he understood the gravity of what the woman brought “within a few minutes,” agreed to represent her and call her by the alias “Sean.”

She “is a very courageous person and is taking a personal risk to hold a trillion-dollar company accountable,” he said.

On Sunday, Frances Haugen revealed herself as the whistle-blower against Facebook. A product manager who worked on the civic misinformation team at the social network before leaving in May, she has used the documents she amassed to expose how much the company knew about the harms that it was causing and provided the evidence to lawmakers, regulators and the news media.

In an interview with “60 Minutes,” Ms. Haugen, 37, said, “I’ve seen a bunch of social networks and it was substantially worse at Facebook than what I had seen before.” She added, “Facebook, over and over again, has shown it chooses profit over safety.”

Ms. Haugen gave many of the Facebook documents to The Wall Street Journal, which last month began publishing the findings. The revelations — including that Facebook knew Instagram was worsening body image issues among teenagers and that it had a two-tier justice system — have spurred criticism from lawmakers, regulators and the public.

Ms. Haugen has also filed a whistle-blower complaint with the Securities and Exchange Commission, accusing Facebook of misleading investors on various issues with public statements that did not match the company’s internal actions. And she has talked with lawmakers such as Senator Richard Blumenthal, a Democrat of Connecticut, and Senator Marsha Blackburn, a Republican of Tennessee, and shared subsets of the documents with them.

The spotlight on Ms. Haugen is set to grow brighter. On Tuesday, she is scheduled to testify in Congress about Facebook’s impact on young users.

Ms. Haugen’s actions were a sign of how Facebook has turned increasingly leaky. As the company has grown into a behemoth with over 63,000 employees, some of them have become dissatisfied as it has lurched from controversy to controversy over data privacy, misinformation and hate speech.

In 2018, Christopher Wylie, a disgruntled former employee of the consulting firm Cambridge Analytica, set the stage for those leaks. Mr. Wylie spoke with The New York Times, The Observer of London and The Guardian to reveal that Cambridge Analytica had improperly harvested Facebook data to build voter profiles without users’ consent.

In the aftermath, more of Facebook’s own employees started speaking up. Later that same year, Facebook workers provided executive memos and planning documents to news outlets including The Times and BuzzFeed News. In mid-2020, employees who disagreed with Facebook’s decision to leave up a controversial post from President Donald J. Trump staged a virtual walkout and sent more internal information to news outlets.

“I think over the last year, there’ve been more leaks than I think all of us would have wanted,” Mark Zuckerberg, Facebook’s chief executive, said in a meeting with employees in June 2020.

Facebook has already tried to preemptively push back against Ms. Haugen. On Friday, Nick Clegg, Facebook’s vice president for policy and global affairs, sent employees a 1,500-word memo laying out what the whistle-blower was likely to say on “60 Minutes” and calling the accusations “misleading.” On Sunday, Mr. Clegg appeared on CNN to defend the company, saying that the platform reflected “the good, the bad and ugly of humanity” and that it was trying to “mitigate the bad, reduce it and amplify the good.”

Her personal website said Ms. Haugen was “an advocate for public oversight of social media.” She was born in Iowa City, Iowa, studied electrical and computer engineering at Olin College and got an M.B.A. from Harvard. She then worked on algorithms at Google, Pinterest and Yelp. At Facebook, she handled democracy and misinformation issues, as well as working on counter-espionage, according to the website.

Ms. Haugen’s complaint to the S.E.C. was based on her document trove and consisted of many cover letters, seven of which were obtained by The Times. Each letter detailed a different topic — such as Facebook’s role in spreading misinformation after the 2020 election; the impact its products have on teenagers’ mental health; and its disclosures about user demographics and activity — and accused the company of making “material misrepresentations and omissions in statements to investors and prospective investors.”

The letters compared public statements and disclosures to lawmakers made by Mr. Zuckerberg and other top Facebook executives to the company’s internal research and documents. In one cover letter, Ms. Haugen said Facebook contributed to election misinformation and the Jan. 6 insurrection at the U.S. Capitol.

While “Facebook has publicized its work to combat misinformation and violent extremism relating to the 2020 election and insurrection,” Ms. Haugen’s documents told a different story, the cover letter read. “In reality, Facebook knew its algorithms and platforms promoted this type of harmful content, and it failed to deploy internally recommended or lasting countermeasures.”

Mr. Tye said he had been in touch with the S.E.C.’s whistle-blower office and division of enforcement regarding Facebook. The S.E.C. typically provides protections for corporate tipsters that shield them from retaliation. The agency also provides awards of 10 percent to 30 percent to whistle-blowers if their tips lead to successful enforcement actions that yield monetary penalties of more than $1 million.

The S.E.C. did not respond to a request for comment.

After filing the S.E.C. complaint, Ms. Haugen and her legal team contacted Mr. Blumenthal and Ms. Blackburn, Mr. Tye said. The lawmakers had held a hearing in May about protecting children online, focusing on how companies like Facebook were collecting data through apps like Instagram.

In August, Mr. Blumenthal and Ms. Blackburn sent a letter to Mr. Zuckerberg asking Facebook to disclose its internal research about how its services were affecting children’s mental health. Facebook responded with a letter that played up its apps’ positive effects on children and deflected questions about internal research.

But documents from Ms. Haugen showed that Facebook’s researchers have performed many studies on the effects that its products can have on teenagers, Mr. Blumenthal said in an interview.

Facebook had engaged in “concealment and deception,” he said. “If Facebook really wants to be credible, they should release all the documents.” In tweets on Friday, Mr. Blumenthal also said that the whistle-blower had provided documents about Facebook and Instagram that were “damning.”

Some of Ms. Haugen’s Facebook documents have also been distributed to the state attorneys general for California, Vermont, Tennessee, Massachusetts and Nebraska, Mr. Tye said.

But he said the documents were not shared with the Federal Trade Commission, which has filed an antitrust suit against Facebook. That’s because Ms. Haugen “generally does not see antitrust as the most important policy approach,” Mr. Tye said. “She wants to see meaningful regulatory reform focused on transparency and accountability.”

Ms. Haugen has also spoken to lawmakers in France and Britain, as well as a member of European Parliament. This month, she is scheduled to appear before a British parliamentary committee. That will be followed by stops at Web Summit, a technology conference in Lisbon, and in Brussels to meet with European policymakers in November, Mr. Tye said.