Messenger is now Facebook's third application that has more than half a billion active monthly users.
The main Facebook app has more than a billion, Facebook owned WhatsApp has around the 600 million mark and now Messenger has 500 million.
In a blogpost, Facebook's director of product management, Peter Martinazzi wrote of the achievement: "This is an exciting milestone but with a half billion people relying on Messenger to communicate and connect, it is also a reminder that there is so much left for us to do."
In a move that proved widely unpopular, Facebook gave users not choice but to download the standalone Messenger application by removing the messaging service from Facebook proper.
It's likely that Messenger would never had hit such a milestone had the users of the main app not been forced into downloading it.
You can see how effective this method proved by observing the fact that Messenger only had 200 million active monthly users in April; the number of users has more than doubled in seven months.
Messenger and the Facebook proper are among the most frequently downloaded applications in the iOS App Store, but both have awful rating of 1.5/5 stars, which has a lot to do with the fact they made messaging a stand alone service.