The change in global smoking trends shows that governments' efforts to control tobacco are working "to save lives, protect health, beat tobacco," the WHO said in a report.
It promised to work closely with countries to maintain the downward trend.
"For many years now we had witnessed a steady rise in the number of males using deadly tobacco products. But now, for the first time, we are seeing a decline in male use, driven by governments being tougher on the tobacco industry," Tedros Adhanom Ghebreyesus, the WHO's Director-General, said in a statement about the report's findings.
Smoking causes lung cancer and other respiratory illnesses and is a major risk factor for cardiovascular diseases such as stroke and heart disease, as well as for mouth, throat and other types of cancer.
Every year, more than 8 million people die from tobacco use, according to WHO data. More than 7 million of those deaths are from direct tobacco use while around 1.2 million are due to non-smokers being exposed to second-hand smoke.
In 2018, some 60 million fewer people around the world smoked or used tobacco compared to 2000, the WHO's report said, with the overall number of tobacco users falling to 1.337 billion people globally in 2018 from 1.397 billion in 2000.
"Fewer people are using tobacco, which is a major step for global public health," said Vinayak Prasad, head of WHO’s tobacco control unit.
This decline had previously largely been driven by fewer women and girls smoking, the WHO said - with the number of male tobacco users rising by around 40 million to 1.093 billion between 2000 and 2018.
But this latest report showed the number of male tobacco users has stopped growing and is projected to decline. By 2020, the report said, there will be 10 million fewer tobacco users overall - male and female - than in 2018, and by 2025, that number will drop by another 27 million people.The WHO global tobacco report covers use of cigarettes, pipes, cigars, waterpipes, smokeless tobacco products such as bidis and cheroots, and heated tobacco products.