Fa Ngum founds the kingdom of Lan Xang

According to the Lao chronicles, Fa Ngum, born in 1316 into the ruling house of Muang Sua, grew up in exile at the court of Angkor, where the king gave him his daughter in marriage and, at some time between 1340 and 1350, an army to win back the kingdom of his fathers. Marching up the Mekong from the south, he took the Lao principalities one after another, fixed a frontier with Đại Việt along the watershed between the Mekong and the Red River, and came down on Muang Sua, where he was proclaimed king. After campaigns against Lan Na and Vientiane and on the Khorat Plateau he returned there for his solemn coronation, in 1353 — a date that George Coedès thought had most probably been transmitted correctly — which marks the founding of the kingdom of Lan Xang Hom Khao, ‘a million elephants and the white parasol’. Coedès linked the rise of the Lao state with the weakening of Sukhothai.

On the Khorat Plateau, the Nithan Khun Borom says, the king of Ayutthaya halted him by recalling that they were “brothers since Borom”, offered him territory and promised him a daughter in marriage (the Phongsawadan places this campaign and the border agreement with Đại Việt after the coronation); Coedès warned that the details of the chronicle still need confirmation from other evidence. To Coedès's knowledge, the only mention of Fa Ngum in an inscription is in a Sukhothai text written after 1359, which names “Chao Phraya Fa Ngom” as Sukhothai's neighbour on the Mekong. A mission of monks and artisans that Fa Ngum sent to Cambodia under his old tutor Maha Pasaman brought back sacred texts and the Phra Bang image of the Buddha, which later gave Luang Prabang its name; the historian Michel Lorrillard, however, traces the tradition that Buddhism reached Lan Xang under Fa Ngum to a 16th-century Pali text and calls his reign semi-legendary. Deposed about 1371–1373 in favour of his son Samsenthai, Fa Ngum died in exile at Nan.