The Facebook-owned company announced the milestone in a blog post. Instagram said that more than 80% of the total were from outside the US.
When Facebook acquired the photo-sharing platform in 2012 for $1bn (£681m), it had around 30m users. The deal was the largest for a then profitless startup since Google paid $1.65bn (£1.12bn) for YouTube in 2006.
Data published last week as part of a report from Criteo on the state of mobile commerce in the UK showed that Instagram users were among the most enthusiastic mobile shoppers.
Fifty-six per cent of the app’s daily users said they had previously bought on mobile, compared to 35% of daily Facebook users, and just 17% of non-Facebook users.
Daily Instagram users were also more than twice as likely to say they bought clothes on mobile as the average person.
In March this year, Facebook had 1.65bn monthly active users – about 22% of the world’s population. The world’s largest country by population, China, has 1.36bn people.