Cambridge Analytica, the political consultancy at the centre of the Facebook data-sharing scandal, is shutting down.
The firm was accused of improperly obtaining personal information on behalf of political clients.
According to Facebook, data about up to 87 million of its members was harvested by a quiz app and then passed on to the political consultancy.
The social network said its own probe into the matter would continue.
"This doesn't change our commitment and determination to understand exactly what happened and make sure it doesn't happen again," said a spokesman.
"We are continuing with our investigation in cooperation with the relevant authorities."
What are the accusations against Cambridge Analytica?
The company has been accused of using the personal data of millions of Facebook users to sway the outcome of the US 2016 presidential election and the UK Brexit referendum.
In March, Channel 4 aired undercover footage of Cambridge Analytica's CEO, Alexander Nix, giving examples of how the firm could swing elections around the world with underhand tactics such as smear campaigns and honey traps.
The UK-based company, which denies any wrongdoing, has an extensive record of working abroad on many election campaigns, including in Italy, Kenya and Nigeria.
Why does it say it is shutting?
Clarence Mitchell, a spokesman for Cambridge Analytica, referred the BBC to a statement on the firm's website.
"Over the past several months, Cambridge Analytica has been the subject of numerous unfounded accusations and, despite the company's efforts to correct the record, has been vilified for activities that are not only legal, but also widely accepted as a standard component of online advertising in both the political and commercial arenas," it said.
"Despite Cambridge Analytica's unwavering confidence that its employees have acted ethically and lawfully... the siege of media coverage has driven away virtually all of the company's customers and suppliers.
"As a result, it has been determined that it is no longer viable to continue operating the business."
The statement added that its parent company SCL Elections was also commencing bankruptcy proceedings.
The sting in the tail
By the BBC's technology correspondent Rory Cellan-Jones, in California
When the news of Cambridge Analytica's demise broke here at Facebook's F8 developer conference, it is safe to say few tears were shed.
The scandal over data misuse has been a crisis not just for Facebook but for the thousands of external developers whose access to data has been curbed in response to the affair.
But if they were tempted to celebrate there was a sting in the tail in the political consultancy's statement. It claimed that what it did was not only legal but was standard practice in the world of online advertising.
That rang true to some people in this world and there may be more evidence of such practices as Facebook continues its audit of apps.
Cambridge Analytica may be gone but as more stones are lifted there may be more unpleasant surprises to come about the use and misuse of personal data.
Is this the end?
The UK's Financial Times newspaper says it has spoken to another ex-employee of Cambridge Analytica, on condition of anonymity, who said they were sure the company would emerge "in some other incarnation or guise".
The Observer journalist whose investigation first exposed the data privacy scandal has suggested that the public remain sceptical.
Remember. SCL & Cambridge Analytica are disinformation specialists. What exactly are they shutting down & why? https://t.co/KKsBYkCCTz— Carole Cadwalladr (@carolecadwalla) May 2, 2018
The chair of a UK parliament committee investigating the firm's activities also raised concerns about Cambridge Analytica and SCL Elections' move.
"They are party to very serious investigations and those investigations cannot be impeded by the closure of these companies," said Damian Collins MP.
"I think it's absolutely vital that the closure of these companies is not used as an excuse to try and limit or restrict the ability of the authorities to investigate what they were doing."
Cambridge Analytica and SCL group cannot be allowed to delete their data history by closing. The investigations into their work are vital— Damian Collins (@DamianCollins) May 2, 2018
What action had it taken already?
Cambridge Analytica's chief executive Alexander Nix was suspended in March after the Channel 4 News footage was aired.
Last month, Cambridge Analytica said it had only licensed 30 million records belonging to US citizens from the quiz app's creator Dr Aleksandr Kogan, and that they had not been used in the US presidential election.
The firm added that it had since deleted all the information despite claims to the contrary by others.
Who funded Cambridge Analytica?
One of Cambridge Analytica's major investors is the US hedge fund billionaire Robert Mercer.
He is said to have put $15m (£11m) into the business, according to the Guardian.
Mr Mercer, a former computer scientist, is also a major donor to the US Republican Party and helped support Donald Trump's election campaign.
He has never given an interview about his political views and is not thought to have commented publicly about the data-harvesting scandal.
What is the Brexit link?
Earlier on Wednesday, a cyber-security specialist presented evidence to the UK parliament's Digital, Culture, Media and Sport Committee.
Chris Vickery linked SCL and Cambridge Analytica to AggregateIQ - a Canadian data analytics firm, which Facebook has also suspended from using its platform.
He added that "beyond a shadow of a doubt" AggregateIQ had been involved in "some form of collaboration or co-ordination" between various pro-Brexit groups during the UK's EU referendum campaign.
AIQ denies ever being part of Cambridge Analytica, its parent company SCL or accessing improperly obtained Facebook data.
And representatives from Vote Leave and Leave.EU have repeatedly denied any wrongdoing.
But the Electoral Commission and Information Commissioner's Office are conducting their own investigations into the Canadian firm's operations.
The ICO has also issued a statement about Cambridge Analytica's closure.
"The ICO will continue its civil and criminal investigations and will seek to pursue individuals and directors as appropriate and necessary even where companies may no longer be operating," it said.
"We will also monitor closely any successor companies using our powers to audit and inspect, to ensure the public is safeguarded."
How the scandal unfolded
17 March: The Observer and the New York Times publish accounts by Cambridge Analytica's ex-employee Christopher Wylie, saying 50 million Facebook accounts were improperly harvested by the company
23 March: The UK's data watchdog is granted a warrant to search Cambridge Analytica's office
27 March: Christopher Wylie appears in front of a committee of UK MPs
4 April: Facebook says it now believes up to 87 million people's data was improperly shared with Cambridge Analytica
10 April: Facebook CEO Mark Zuckerberg is questioned by US lawmakers about the scandal
17 April: Alexander Nix, the former boss of Cambridge Analytica, refuses to appear before British MPs
26 April: The UK parliamentary committee threatens to issue Mark Zuckerberg with a "formal summons for him to appear when he is next in the UK" as questions remain unanswered
2 May: Cambridge Analytica announces its closure