"This is about our responsibility," Biden said before the meeting of the Group of Seven, or G-7, leaders in Britain. The G-7 is a group of seven of the world's wealthiest democracies.
"We're doing this to save lives, to end this pandemic, and that's it," Biden said as he asked the rest of the G-7 to join the U.S. effort.
The donation comes on top of another 80 million doses that Biden had already promised to other countries.
Johns Hopkins University estimates about 2.2 billion people have been vaccinated out of a world population of nearly 8 billion. Most of them are in wealthy countries in Europe, Israel, Bahrain and the U.S.
Demand for the shots has fallen in the U.S. recently, leading to calls for the country to share its vaccine with others.
The U.S. will buy and donate 500 million doses of the Pfizer vaccine through the United Nations-backed COVAX partnership. They will be sent to 92 poorer countries and the African Union.
A U.S. official told Reuters the vaccines will cost $3.5 billion, in addition to the $4 billion the U.S. has donated to COVAX so far.
White House officials said the vaccines will be shipped starting in August. The goal is to donate 200 million by the end of the year. The remaining 300 million doses will be shipped in the first half of 2022.
Jen Psaki is a White House spokesperson. She told CBS News on Thursday that the U.S. "is in this position because we've had so much success at home vaccinating Americans."
The U.S. led the world in new cases of COVID-19 and deaths over much of the last year. But the country is on its way to a strong recovery after a successful vaccination program. The average numbers of new cases and deaths are now at their lowest point since the beginning of the pandemic.
U.S. officials hope the meeting will end with a promise from the G-7 countries to do more to vaccinate the world.
China and Russia have also shared their own vaccines with poorer countries with mixed success. But, the mRNA vaccines, produced by American drug companies Pfizer and Moderna, have shown to be more effective against the coronavirus and its variants.
Biden's plans drew strong praise from Tom Hart. He is head of The ONE Campaign, an organization that seeks to end poverty. He said Biden's announcement was "the kind of bold leadership that is needed to end this global pandemic."
But others think the G-7 nations need to do more and share vaccines with the world.
Niko Lusiani is with the anti-poverty group Oxfam.
"At the current rate of vaccinations, it would take low-income countries 57 years to reach the same level of protection as those in G-7 countries," he said.
"That's not only morally wrong, it's self-defeating given the risk posed by coronavirus mutations."
I'm Dan Novak.