Charles III is head of state of 15 Commonwealth realms and has had 22 prime ministers throughout his reign. Within the Westminster system in each realm, the King's government is headed by a prime minister. Appointment and dismissal of prime ministers are common reserve powers that can be exercised by the King or his governors-general. To date, seven new prime ministers have been appointed during the reign of Charles III, the first being Rishi Sunak as Prime Minister of the United Kingdom on 25 October 2022 and the most recent being Mark Carney as Prime Minister of Canada on 14 March 2025.
This list does not cover Commonwealth nations that are not Commonwealth realms, as Charles is not head of state in these nations. Nor does it cover holders of offices of prime minister in sub-national entities such as states, dependencies, or provinces.
Justin Trudeau was the incumbent prime minister when Charles III became King.
Jacinda Ardern was the incumbent prime minister when Charles III became King.
Manasseh Sogavare was the incumbent prime minister when Charles III became King.
Kausea Natano was the incumbent prime minister when Charles III became King.
Liz Truss was the incumbent prime minister when Charles III became King.