The
California-based firm announced the milestone just six years after it was
founded by ex-Yahoo! employees Brian Acton and Jan Koum.
The
app's popularity has stemmed from its allowing groups of people to stay in
touch simultaneously without having to enter contact details.
As
well as text messages, users can also share photos, videos and other media.
It
also offers a similar secure messaging service to the BlackBerry and has become
more popular as the Canadian phone maker has seen its handsets fall in
popularity compared to those made by other smart phone makers.
It has also proved popular in the US where mobile phone
customers often have to pay for text messages.
More
than half of its subscribers have been added in the last 21 months, according
to Forbes.
A
message on the app's blog section said: "One billion people are using
WhatsApp. That's nearly one in seven people on Earth.
"We
are proud of this milestone, and we're humbled by the extraordinary ways all of
you have used WhatsApp.
"WhatsApp
began as a simple idea: ensuring that anyone could stay in touch with family
and friends anywhere on the planet, without costs or gimmicks standing in the
way.
"So
even as we celebrate this achievement, our focus remains the same.
"Every
day, our team continues to work to improve WhatsApp's speed, reliability,
security and simplicity. We're excited to see how far we've come. But now, it's
back to work – because we still have another 6 billion people to get on
WhatsApp."
WhatsApp
was bought by Facebook in February 2014 for $19bn (£12bn).
It
is popular in India, which has the largest number of users for a country, but
faces competition in Asia from other messaging services like WeChat and Viber.