It was used recently to launch B-2 bomber attacks on Houthi rebels in Yemen during the Gaza war.
Opposition politicians in the UK have been critical of the deal, which would see Britain pay Mauritius £101 million (US$136 million) annually for 99 years.
The net cost over the length of the lease would be around £3.4 billion if inflation was factored in, according to the government.
Kemi Badenoch, leader of the opposition Conservative party, said: “Unfortunately on this issue President Trump is right.”
“Thank goodness Trump has vetoed the surrender of the Chagos islands,” said Nigel Farage, the leader of the hard-right Reform UK party.
But Ed Davey, leader of the centrist Liberal Democrat party, said in a post on X that Prime Minister Keir Starmer should begin to stand up to the US leader.
“This shows Starmer’s approach to Trump has failed,” he said. “The Chagos seal was sold as proof the government could work with him. Now it’s falling apart. It’s time for the government to stand up to Trump – appeasing a bully never works.”