The 73-year-old megastar beaten his contemporaries Shah Rukh Khan (19.6 million), Salman Khan (17.8 million), Aamir Khan (17.6 million) and Priyanka Chopra (14 million) with his new milestone.
Bachchan's Twitter account became live in May, 2010 and ever since has been a one stop destination for his fans to connect, interact and engage with the actor.
"#AB21Million ... Yohohohohohohohohohhhooooooo ..," he tweeted.
On Twitter, the "Wazir" actor is followed by stars like Mukesh Bhatt, Sridevi, Dilip Kumar, Madhuri Dixit Nene among others. Bachchan has so far made over 49 thousand tweets.