king of Cambodia from 1904 until his death. He was a figurehead for the French colonial administration, which had secured the protectorate over Cambodia in a treaty signed by Sisowath's half-brother Norodom in 1863.

With Norodom, Sisowath received his education under the surveillance of the Thai sovereign at Bangkok because Siam (Thailand), with Vietnam, had long held Cambodia in vassalage and chosen Cambodian sovereigns. Sisowath remained at Bangkok until his father, King Duong, died in 1860. He then went to Oudong, the old Cambodian capital just north of Phnom Penh, to prevent his younger half-brother Si Votha from seizing the throne. He forced Si Votha out of Oudong, but the Thais recalled him to Bangkok and hastily installed the more compliant Norodom on the throne.

When the French won partial control of Vietnam in 1862, they claimed a protectorate over Cambodia as well. Norodom was crowned with French consent, and Sisowath withdrew to Saigon, where he was subsidized by the French, who could threaten Norodom with the prospect of installing Sisowath in his place.

Sisowath remained in Saigon until 1867, when he was called to quell anti-French uprisings in Cambodia. He thereafter remained in Phnom Penh and gave his support to the French colonial regime. Norodom died in 1904, and the French placed Sisowath on the throne. In 1906 he visited the Colonial Exhibition at Marseille and toured France. Upon his death, he was succeeded by his son Monivong.