The long era of absolute monarchy was brought to a sudden end on June 24, 1932, by a bloodless coup d'etat engineered by a group of civil servants and army officers with the support of army units in the Bangkok area. The action was specifically directed against ministers of the conservative royal government and not against the person of the king. Three days after the coup a military junta put into effect a provisional constitution drawn up by a young law professor, Pridi Phanomyong. Prajadhipok reluctantly accepted the new situation that had stripped him of his political power but in principle had left the prestige of the monarchy unimpaired.

The coup leaders, who were known as the "promoters," were representative of the younger generation of Western-oriented political elite that had been educated to be instruments of an absolute monarchy--an institution they now viewed as archaic and inadequate to the task of modern government. The principals in the coup identified themselves as nationalists, and none questioned the institution of the monarchy. Their numbers included the major figures in Thai politics for the next three decades. Pridi, one of the country's leading intellectuals, was the most influential civilian promoter. His chief rival among the other promoters was Phibun, or Luang Plaek Phibunsongkhram, an ambitious junior army officer who later attained the rank of field marshal. Phahon, or Phraya Phahonphonphayuhasena, the senior member of the group, represented old-line military officers dissatisfied with cuts in appropriations for the armed forces. These three exercised power as members of a cabinet, the Commissariat of the People, chosen by the National Assembly that had been summoned by the promoters soon after the coup. To assuage conservative opinion, a retired jurist, Phraya Manopakorn, was selected as prime minister.

A permanent constitution was promulgated before the end of 1932. It provided for a quasi-parliamentary regime in which executive power was vested in a unicameral legislature, the National Assembly, of which half of the members were elected by limited suffrage and half appointed by the government in power. The constitution provided that the entire legislature would be elected when half of the electorate had received four years of schooling or after ten years had elapsed, whichever came first. The National Assembly was responsible for the budget and could override a royal veto. Real power resided with the promoters, however, and was exercised with army backing through their political organization, the People's Party.