President Mohamed Muizzu's office told the BBC the Maldives had expressed its opposition to the "deeply concerning" deal in two written objections and a phone call with Deputy Prime Minister David Lammy.
The nation of tropical islands in the Indian Ocean is asserting sovereignty over the Chagos Islands and is threatening international legal action to press its claim.
UK Foreign Office minister Stephen Doughty has said the sovereignty of the Chagos Islands is a matter for Britain and Mauritius, not the Maldives.
A government source said international courts had already considered the question of sovereignty over the Chagos Islands and found in favour of Mauritius.
The Chagos Islands - officially known as the British Indian Ocean Territory - are located in the Indian Ocean and the UK has controlled them since the early 19th Century.
Last year, the UK government agreed to transfer control of the territory to Mauritius, paying an average cost of £101m a year to lease a joint UK-US military base on the largest island.
Mauritius has long claimed the islands and has pursued international legal action.
Labour ministers have argued that if a deal with Mauritius was not struck, the future of the military base would be threatened by international legal rulings.
But the deal has not yet been confirmed in UK law and appears to be indefinitely on hold, after US President Donald Trump urged Prime Minister Sir Keir Starmer not to give up the territory.
The Maldives opposes Mauritian control of the Chagos Islands and argues it has historical claims to the archipelago dating back centuries.
In a detailed statement sent to the BBC, Muizzu's office outlined his country's position on the Chagos Islands and its diplomatic engagements with the British government.
The Maldives wrote to the British government in November 2024 and January 2026 to formally object to its deal with Mauritius.
"These diplomatic communications articulate the government's firm position: the decision by the British government to proceed in sole consultation with Mauritius - without due consideration of Maldivian interests - is deeply concerning," the statement said.
