The World Health Organization on Friday approved Johnson & Johnson's Covid-19 vaccine, after already authorising the jabs made by Pfizer-BioNTech and Oxford-AstraZeneca.
"Every new, safe and effective tool against Covid-19 is another step closer to controlling the pandemic," WHO chief Tedros Adhanom Ghebreyesus said in a statement.
The news comes after the single-dose jab won approval from the European Union on Thursday.
It has also received the green light from regulators in the United States, Canada and South Africa.
The World Health Organisation said the J&J jab had been granted an "emergency use listing" which assesses the suitability of new health products during public health emergencies, and is quicker than the regular licensing system.
WHO authorisation paves the way for the jabs to be used as part of the Covax initiative aimed at ensuring equitable access to vaccines in poorer countries.
Some 500 million doses of the J&J jabs have been promised to the facility and the WHO hopes it can be rolled out through the scheme from July, if not earlier.
"We hope this new vaccine will help to narrow vaccine inequalities, and not deepen them," Tedros told a briefing.
Clinical trials have found that the J&J shot was 67 percent effective at preventing people from getting Covid-19.
But that result considered all forms of Covid-19. The jab proved 85.4 percent effective at preventing severe disease.
And since this is a single-dose jab, WHO said it expected it to facilitate vaccination logistics in all countries.
"The sample data from large clinical trials shared by the company also shows that the vaccine is effective in older populations," it said.