Thai city-states gradually became independent of the weakened Khmer Empire. Sukhothai was originally a trade center in Lavo—itself under the suzerainty of the Khmer Empire—when Central Thai people led by Pho Khun Bang Klang Hao, a local leader, revolted and gained their independence. Bang Klang Hao took the regnal name of Si Inthrathit and became the first monarch of the Phra Ruang dynasty. The kingdom was centralized and expanded to its greatest extent during the reign of Ram Khamhaeng the Great (1279–1298), who some historians considered to have introduced Theravada Buddhism and the initial Thai script to the kingdom. Ram Khamhaeng also initiated relations with Yuan China, through which the kingdom developed the techniques to produce and export ceramics like sangkhalok ware.

After the reign of Ram Khamhaeng, the kingdom fell into decline. In 1349, during the reign of Li Thai (Maha Thammaracha I), Sukhothai was invaded by the Ayutthaya Kingdom, a neighboring Thai polity. It remained a tributary state of Ayutthaya until it was annexed by the kingdom in 1438 after the death of Borommapan. Despite this, the Sukhothai nobility continued to influence the Ayutthaya monarchy in centuries after through the Sukhothai dynasty. Sukhothai is traditionally known as "the first Thai kingdom" in Thai historiography, but current historical consensus agrees that the history of the Thai people began much earlier.