Eighteen enforcement officers working for the UK's information commissioner are searching the London headquarters of Cambridge Analytica.
The High Court granted the data watchdog a warrant amid claims the firm amassed information about millions of people without their consent, based on a 2014 personality quiz on Facebook.
It is part of a wider investigation into political campaigning.
Both Cambridge Analytica and Facebook deny any wrongdoing.
Cambridge Analytica's acting chief executive, Alexander Tayler, said the company has been in touch with the Information Commissioner's Office (ICO) since February 2017 and it remained committed to helping the investigation.
In a statement, he said checks in 2015 showed all the Facebook data had been deleted but the company was now undertaking an independent third-party audit to verify none remained.
Cambridge Analytica chief executive Alexander Nix was suspended on Tuesday after footage broadcast on Channel 4 appeared to show him suggesting tactics his company could use to discredit politicians online.
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The ICO applied for the warrant to access to the databases and servers of Cambridge Analytica.
Information Commissioner Elizabeth Denham has said she was looking at whether personal data was acquired in "an unauthorised way", whether there was sufficient consent to share the data, what was done to safeguard it and whether Facebook acted robustly when it found out about the loss of the data.
Claims over whether Cambridge Analytica used the personal data of millions of Facebook users to sway the outcome of the US 2016 presidential election and the UK Brexit referendum have also been raised.
The company denies any of the data harvested in the 2014 Facebook quiz created by an academic was used in its work for Donald Trump's campaign.
Meanwhile, the director of Vote Leave has denied allegations of links between his campaign and Cambridge Analytica. Dominic Cummings said claims by the Observer newspaper are "factually wrong, hopelessly confused, or nonsensical".
In a separate development, Brittany Kaiser, Cambridge Analytica's former business development director, has told the Guardian the firm carried out data analysis for Leave.EU, the rival Brexit campaign to Vote Leave that was fronted by Nigel Farage.
Cambridge Analytica said it did "no paid or unpaid work" for Leave.EU.