The global body said new information showed they could provide "a barrier for potentially infectious droplets".
Some countries around the world already recommend or mandate the wearing of face coverings in public.
The WHO had previously argued there was not enough evidence to say that healthy people should wear masks.
Dr Maria Van Kerkhove, the WHO's technical lead expert on Covid-19, told Reuters news agency the recommendation was for people to wear a "fabric mask - that is, a non-medical mask".
The organisation had always advised that medical face masks should be worn by people who are sick and those caring for them.
Globally, there have been 6.7 million confirmed coronavirus cases and nearly 400,000 deaths since the outbreak began late last year, according to data compiled by Johns Hopkins University.
What is the WHO's advice?
The organisation said its new guidance had been prompted by studies over recent weeks. "We are advising governments to encourage that the general public wear a mask," Dr Van Kerkhove said.
At the same time, the WHO stressed that face masks were just one of a range of tools that could be used to reduce the risk of transmission - and that they should not give people a false sense of protection.
"Masks on their own will not protect you from Covid-19," said WHO Director-General Tedros Adhanom Ghebreyesus.