The White House confirmed the pledge while underscoring the U.S.'s decision to commit 500 million doses, or half of the allotment from the G-7 and guest countries.
Most of the G7 heads of state and government will reconvene on Monday in Brussels for a North Atlantic Treaty Organisation meeting, before Biden heads on to his first summit with President Vladimir Putin in Geneva, vowing to deliver a blunt appraisal of Russian behaviour.
US President Joe Biden and his colleagues from Britain, Canada, France, Germany, Italy and Japan will sit down for their first face-to-face gathering in almost two years, after the pandemic wiped out last year's summit.
UK Prime Minister Boris Johnson opened the G7 Summit in Cornwall on Friday with a message for the world leaders to "learn lessons" from the pandemic and warned that it is vital not to repeat mistakes of the "the last big economic recession of 2008" when the recovery was not uniform across all parts of society.
Leaders are also to come up with a plan to extend vaccine manufacturing.
Canadian Prime Minister Justin Trudeau's hair flapped in the wind before German Chancellor Angela Merkel took the platform to elbow-bump Mr. Johnson and Mrs. Johnson in pandemic fashion, though no one wore a mask.
UK Prime Minister Boris Johnson, who is hosting the three-day summit in the coastal village of Carbis Bay, announced his country would provide 100 million surplus doses, majority to be distributed through the COVAX vaccine-sharing program.
"We've been calling to target the vulnerable around the world. So let's assume we get to one billion by the end, that will be extraordinarily welcome".
Here's when it takes place, what the summit is for and what to expect. "Global solutions are needed", according to a draft of a "Carbis Bay Health Declaration" seen by dpa.
In the evening, the leaders are scheduled to attend a reception hosted by Queen Elizabeth II and her son, Prince Charles, during which environmental protection and fighting climate change are on the agenda.
It will be held in the coastal region of Carbis Bay in Cornwall in the UK.
At the end of the summit, the group typically signs and publishes a final document about the meeting, and their goals and objectives.
On the first day, leaders will also focus on questions such as COVID-19 vaccine donations and financial aid to build vaccine production sites around the world.
It is the first major worldwide summit for Biden, which he is attending as part of a one-week Europe trip.
Leaders of the G-7 countries - Britain, Canada, France, Germany, Italy, and Japan, along with the US - are also expected to endorse a strong global minimum tax of at least 15 percent, according to the White House.
The group has been criticized for being outdated, considering two of the largest countries in the world, India and China, are not included.
This year, the United Kingdom has the G7 Presidency and has also invited Australia, India, South Korea and South Africa as guest countries to attend this year's Summit.
Johnson has said he hopes this will make the summit more of a conference of leading democracies.