The change in policy, WhatsApp's first since the deal, will allow for more relevant advertisements and friend recommendations on Facebook, according to a WhatsApp blog post.
WhatsApp, however, sought to reassure users by saying that it would not sell, share, or give users' phone numbers to advertisers.
WhatsApp said users could choose not to share account information with Facebook.
The shared data will also help WhatsApp track information about how often people use its services and tackle spam on the service, it said on Thursday.
WhatsApp, which has more than 1 billion users, will also explore ways for businesses to send messages using its platform over the next several months, it said.