The 25-year-old has left behind teen sensation Justin Bieber who was recently announced as the most followed celebrity with 16 mn online fans, reports contactmusic.com.
The "Poker Face" singer announced the big news Monday posting: "Can't believe I have 18,000,000 TwitterMonsters, really rad, was just a few years ago I had barely any."
Gaga currently has 18,133,842 followers.