Sin Byu Shin, leaving a viceroy with a small garrison to rule the country, withdrew his army to meet a threatened Chinese invasion of Burma and once again Siam fell into an interregnum of anarchy, with outlying districts setting themselves up as independent while robber bands preyed upon the people. An ex-official named Phraya Taksin, who had deserted his King when Ayuthia seemed likely to fall, gathered about himself a large number of deserters and broken men like himself and, by guile and treachery, soon acquired complete authority in the southeastern provinces, whence, in due time, he appeared before the walls of Ayuthia as a national avenger. Overcoming the garrison and killing the Burmese viceroy, Taksin declared himself King and selected, as the site of his new capital, the village of Tonburi, on the shore of the Chao Phraya opposite the settlement of Bangkok, where a populous city soon came into being. To strengthen his position, however, it was essential that Taksin destroy a legitimate pretender to the throne whose claims had many adherents; this prince had established himself at Khorat and thither the King sent an army with orders to take the city. But in advance of his soldiers he sent secret emissaries who so demoralized the prince's supporters that when the usurper's army appeared at last, the city fell into his hands almost without a struggle and the prince was captured and soon afterward murdered. With this last threat to his power removed, Taksin was able to send out expeditions in all directions and soon made himself undisputed master of the whole country.

The authority of this ruthless man was not to endure long. His appointment of humble relatives to high office offended the nobility, while the popular mind was turned against him by his excesses and by insidious references to his alien ancestry. In 1781, giving out that he was mad, a cabal of his courtiers dethroned him and offered the crown to one of themselves, the son of a secretary to the last kings of Ayuthia. This nobleman, Phraya Chakkri, already popular through his achievements as a royal minister and as a leader of the armies, was readily accepted as King by the people and ascended the throne in A.D. 1782, to found the dynasty which still reigns in Siam.