Facebook will begin connecting with the 87 million users - including 562,455 in India - from Monday if their personal data was "improperly shared" with the British political consultancy firm Cambridge Analytica.
Those affected by the data privacy breach will see a detailed message at the top of their news feeds.
Apart from those affected, over 2 billion Facebook users will also see a link "at the top of their news feed so they can see what apps they use and the information they have shared".
Facebook does not know how Cambridge Analytica and Global Science Research used the data of users because the firms are not its downstream affiliates and may have made independent decisions regarding the data they obtained. This, Facebook said, was "not authorise(d) and breached our policies".
The location of those affected has been identified. But Facebook said the location was "not an indication of voter registration, nationality or citizenship and may not, in some cases, indicate actual place of residence".
"We continue to investigate all apps that had access to large amounts of information before we changed our platform in 2014 to reduce data access and we will conduct a full audit of any app with suspicious activity," a Facebook spokesperson said in a statement last week.
The social media giant informed the Indian government last week about the details of compromised accounts in response to a notice over the user data breach and details of the steps Facebook was taking to ensure safety and prevent misuse of personal data.
A Facebook spokesperson said a possible breach of data of 562,455 users happened after 335 Facebook users in India installed a quiz app, "thisisyourdigitallife" between November 2013 and December 2015.
The app, developed by University of Cambridge psychology researcher Aleksandr Kogan and his company Global Science Research, pulled out data of not only these 335 users but their friends as well as friends of friends also.
Some 335 people in India were said to have installed the app, which is 0.1 per cent of its total worldwide installs.
"We further understand that 562,120 additional people in India were potentially affected, as friends of people who installed the app. This yields a total of 562,455 potentially affected people in India."
The social media giant, however, did not reveal the identity or locations of these 335 users.
After facing mammoth controversy over its users' data breach, the Facebook CEO Mark Zuckerberg is expected to testify before two Congressional committees this week.
Meanwhile, battered by media reports that it "secretly" deleted CEO Mark Zuckerberg's posts from his recipients' inboxes, Facebook is now planning to make its "Unsend" feature - like WhatsApp -- available to its users in the coming months.
In order to prevent election interference on its platform, Facebook has also introduced new changes to increase transparency and accountability for electoral ads and Pages.