Little is known of the history of Phongsaly, but historians believe the Phou Noi left Muang Sing and Burma and arrived in Phongsaly at the end of the 18th century. Groups of Hmong settled there at the end of the 19th century, having migrated from southern China.
In 1895, a Sino-French treaty transferred the Tai Lue's Sipsongpanna principalities of Phongsaly and Muang Sing to French colonial Laos. The French drew new boundaries along the watersheds of the Nam Ou River, and incorporated Sipsongpanna’s east to Phongsaly and French Indochina.
Most of Sipsongpanna went to Yunnan Province, China. Unlike other cities in Laos, Phongsaly features the old quarter with wooden Yunnan architecture now rare to find in Yunnan itself. Most of the people living here belong to the Haw ethnic group, and speak Chinese.
Between 1908 and 1910, the Tai Lue revolted against French colonial authority, but failed, and the French military assumed full authority over Phongsaly by 1916.
In 1936, Sithon Kommadam and and his brother, Kamphanh were jailed in Phongsaly because of their participation in Ong Kommandam’s 1934–1936 armed revolt against the French. After Sithon's release in 1945, he established resistance bases in Phongsaly, soon making contact with the Viet Minh. The Communists came into power in 1954 in the province.
Subsequent to the 1954 Geneva Accords, Pathet Lao forces in Phongsaly province were provided with regrouping zones. Phongsaly was integrated into the Royal Lao Government on 18 December 1957, and became a province in 1975, when Laos won independence. Phongsaly town was not destroyed in the Indochina War.
The capital of Phongsaly Province is Phongsaly Town, which has complicated history. Having served as a Chinese, French, and Vietnamese outpost, the town is surrounded by rolling hills and is built into the side of Phou Fa Mountain.
Sources: Lao Ministry of Information, Culture, and Tourism
Michaud, Jean (2006). Peoples of the Southeast Asian Massif.