The first recorded history of the Lao begins with King Fa Ngum, by legend the 23rd successor of Khoun Lo, who first united Laos in 1353. He established his capital at Luang Prabang and ruled a kingdom called Lan Xang (literally, 'million elephants') that covered much of present-day Thailand and Laos. He also established Buddhism as the state religion.

In the 16th century Lan Xang entered a period of decline caused by dynastic struggles and conflicts with Burma, Siam (now Thailand), Vietnam, and the Khmer Kingdom. By the 18th century, the Siamese and Vietnamese kingdoms were competing for control of Laos. In the 19th century, the Siamese dominated much of what is now Laos and divided it into principalities centred on Luang Prabang, Vientiane, and Champassak. Late in the century, the French, who already controlled present-day Vietnam, supplanted them. In 1899 France established protectorates and direct rule over all of the principalities, and Laos became part of French Indochina. The Franco-Siamese treaty of 1907 defined the present Lao boundary with Thailand.

During World War II the Japanese occupied Indochina. A Lao resistance group, Lao Issara, was formed to prevent the return of the French. Independence was achieved in 1953 but conflict persisted between royalist, neutralist and communist fractions. The US began bombing North Vietnamese troops on the Ho Chi Minh Trail in Eastern Laos in 1964, escalating the conflict between the royalist Vientiane government and the communist Pathet Lao who fought alongside the North Vietnamese. By the time a cease-fire was negotiated in 1973 Laos had the dubious reputation of being the most heavily bombed country on a per capita basis in the history of warfare.

Acoalition government was formed but when Saigon fell in 1975 most of the royalists left for France. On 2 December 1975 the monarchy was abolished and the communist Lao People's Democratic Republic was established, and the Pathet Lao peacefully took control of the country. Lao remained closely allied with the Vietnamese communists during the 1980s. Laos cemented ties with its neighbours when it was welcomed into ASEAN in July 1997. There is no political pluralism in Laos; the only party allowed being the Lao People's Revolutionary Party (LPRP).