They are now the third most followed team behind Real Madrid and Barcelona.
"We are delighted to have engaged so many passionate Arsenal fans around the world," said Richard Clarke, managing editor of the club's media group.
"The interest continues to grow and we constantly evolve our approach to keep our fans engaged with what is happening across every aspect of the club."
Arsenal are sixth in the Premier League going into Christmas, 12 points behind leaders Chelsea, who have 4.85m Twitter followers.
They play their next fixture at home to London rivals QPR on Friday.
Mesut Ozil is Arsenal's most followed player on Twitter with 8.59m followers.
Real Madrid's Cristiano Ronaldo is the most popular footballer in the world on Twitter with 32.1m followers.
Wayne Rooney became the first Premier League footballer to reach 10 million Twitter followers in October.
However, Arsenal may lose the lead in the UK.
Manchester United are adding more than 4,000 new followers every day compared to just under 2,400 for Arsenal.
The London club joined Twitter in April 2009 with Manchester United signing up three years later in April 2012.
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Arsenal have become the first Premier League club to reach five million followers on Twitter.