The White House unveiled the allocation for sharing the first 25 million doses with the world.
It plans to share 80 million vaccine doses globally by the end of June.
The Biden administration says 25 per cent will be kept in reserve for emergencies and for the US to share directly with allies and partners.
"As long as this pandemic is raging anywhere in the world, the American people will still be vulnerable," Mr Biden said.
"And the United States is committed to bringing the same urgency to international vaccination efforts that we have demonstrated at home."
Of the first tranche of 25 million doses, the White House said about 19 million will go to Covax.
Approximately six million will be for South and Central America, seven million for Asia, and five million for Africa.
The doses mark a substantial - and immediate - boost to the lagging Covax effort, which to date has shared just 76 million doses with needy countries.
National security adviser Jake Sullivan said the US "will retain the say in terms of where" the doses distributed through Covax ultimately go.
"We're not seeking to extract concessions, we're not extorting, we're not imposing conditions the way that other countries who are providing doses are doing; we're doing none of those things," said Mr Sullivan.
"These are doses that are being given, donated free and clear to these countries, for the sole purpose of improving the public health situation and helping end the pandemic."
The remaining six million will be directed by the White House to US allies and partners including Mexico, Canada, and the Republic of Korea, the West Bank and Gaza, India, Ukraine, Kosovo, Haiti, Georgia, Egypt, Jordan, Iraq and Yemen.
United Nations frontline workers will also receive a share.
The growing US stockpile of Covid-19 vaccines is seen not only as a testament to American ingenuity, but also its global privilege.
The long-awaited vaccine sharing plan comes as demand for shots in the US has dropped significantly.
More than 63 per cent of adults have received at least one dose, and as global inequities in supply have become more glaring.
Scores of countries have requested doses from the United States, but to date only Mexico and Canada have received a combined 4.5 million doses.