The earliest known indigenous culture in Laos was an iron-age megalithic people that lived on the Plain of Jars, at the centre of trade routes to China, Vietnam and points south. The early inhabitants of Laos and the surrounding parts of central and southern Indochina spoke Austroasiatic languages such as Mon and Khmer, while the ancestors of the lowland Lao spoke proto-Tai languages, and were still living in the river valleys of southeastern China.

With the lowlands to the east and northeast densely settled by Vietnamese and Chinese populations, the Tai peoples slowly migrated west and southwest into northern Laos and southern Yunnan, displacing the sparse indigenous population of Austronesian and Austroasiatic groups and forcing them into the less desirable upland areas - where their descendants still live today. This migration of the Tai is reflected in the Lao legend of Khoun Borom , the heavenly first ancestor, a version of which dates this event in 698 AD.