Sir Keir Starmer is due to sign a deal handing the Chagos Islands to Mauritius on Thursday.
Under the terms of the deal Mauritius would gain sovereignty of the islands from the UK, but allow the US and UK to continue operating a strategically important military base on one of the islands for an initial period of 99 years in exchange for a multi-billion pound payment.
As first reported in The Telegraph, the prime minister will attend a virtual signing ceremony with representatives from the Mauritian government on Thursday.
The deal previously appeared to have stalled after a change in government in both Mauritius and the US – where aides to Donald Trump were given time to examine the plan.