The decision "makes the Pfizer/BioNTech vaccine the first to receive emergency validation from WHO since the (novel coronavirus) outbreak began a year ago," WHO said in a statement.
Britain launched its inoculation drive with the US-German vaccine on December 8, with the United States, Canada and EU countries following suit.
"This is a very positive step towards ensuring global access to COVID-19 vaccines," said Mariangela Simao, a top WHO official tasked with ensuring access to medicines.
"But I want to emphasise the need for an even greater global effort to achieve enough vaccine supply to meet the needs of priority populations everywhere," she said in a statement.
WHO said its emergency use listing opens the way for regulators in different countries to approve the import and distribution of the vaccine.
It said it also enables UNICEF, which plays a key logistical role in distributing anti-Covid vaccines, and the Pan-American Health Organization to procure the vaccine for countries that need it.
WHO convened its own experts and those from around the world to review the data on the Pfizer/BioNTech vaccine's "safety, efficacy and quality," weighing the benefits against the risks.
"The review found that the vaccine met the must-have criteria for safety and efficacy set out by WHO, and that the benefits of using the vaccine to address COVID-19 offset potential risks," it said.