He follows Katy Perry (103m) who managed it in June, but is in front of Taylor Swift (85.5m) and Rihanna (79.9m).
Former US president Barack Obama comes in third though with 94.3m.
To celebrate, Bieber has been given his own emoji on the site, which fans can use by using the hashtag #100millionbeliebers.
It all started for him when he was 15 and needed the hits:
Check out my single "ONE TIME" on my myspace and spread the word for me. Thanks www.myspace.com/justinbieber
But his most re-tweeted post was when he wanted to let us all know how he was after he was arrested for drinking under the influence:
YOU ARE ALL WORTHY NO MATTER WHAT ANYONE SAYS >> BE STRONG GOD IS WITH US ALL> MY BELIEBERS CHANGED MY LIFE> I WILL FOREVER BE GRATEFUL
And we've learnt some things about him too:
If I could be any animal I would be a liger.. Cuz there sweet..
Sometimes he can still be really relatable:
gonna nap...yeah i still nap. naps are cool. who doesnt like naps?
Through it all he's stayed humble, despite him having (nearly) the most followers on Twitter:
....that is why i like twitter. i can say it how it is. no one twisting things