The social media giant made no admission of liability but agreed to pay the fine, which was originally imposed in October 2018.
The ICO last year said it would fine Facebook over breaches including the Cambridge Analytica scandal in which user data was harvested from tens of millions of people, including at least one million British users.
Facebook initially appealed the fine and a court ordered the ICO to disclose files about its decision-making process in order to examine potential bias against the social media company.
The ICO appealed against this decision, but both parties have since dropped their appeals.
The investigation is still ongoing.
James Dipple-Johnstone, deputy commissioner for the ICO, said: "The ICO's main concern was that UK citizen data was exposed to a serious risk of harm.
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