Who took oath as the new Prime Minister of the United Kingdom in 2025?

No new Prime Minister of the United Kingdom took office in 2025. Keir Starmer was already Prime Minister, having been appointed by King Charles III on 5 July 2024 after Labour won the UK general election.

There isn’t a separate oath-taking ceremony for the role of prime minister. The monarch appoints the person able to command the confidence of the House of Commons; the Privy Council oath is a separate matter.