Boris Johnson says the UK will start donating coronavirus vaccines to poorer countries in the next few weeks.
More than 100 million surplus doses will be delivered in the next year, he announced ahead of the G7 summit.
US President Joe Biden has promised 500 million doses of Pfizer vaccines to 92 low and middle-income countries and the African Union.
Five million doses will be given by the UK by the end of September, with 25 million more by the end of the year.
The prime minister said: “As a result of the success of the UK’s vaccine programme we are now in a position to share some of our surplus doses with those who need them.
“In doing so we will take a massive step towards beating this pandemic for good.”
He said he hoped his fellow leaders at the summit in Carbis Bay, Cornwall, which starts on Friday, would “make similar pledges so that, together, we can vaccinate the world by the end of next year”.