List of current reigning monarchs by length of reign

This is a list of reigning monarchs sorted by length of service.

This list includes monarchs who do not reign over entire nations, such as Muhammad V of Kelantan, but does not include former monarchs and pretenders, such as Simeon II of Bulgaria; ex officio monarchs such as the president of France and bishop of Urgell, who by virtue of their position are also the co-princes of Andorra; monarchs without physical territories such as the Prince and Grand Master of the Sovereign Military Order of Malta; constituent monarchs such as traditional African rulers; or monarchs whose position is unofficial, such as Tenzin Gyatso, 14th Dalai Lama.

Hassanal Bolkiah is the longest-reigning existing monarch, having been Sultan of Brunei since 5 October 1967. He became the longest-reigning monarch upon the death of Elizabeth II of the United Kingdom on 8 September 2022. Ntfombi, Queen Mother of Eswatini is the only female monarch in the world.