By the time Ayutthaya was invaded by Burma at the end of King Ekatat's reign, King Tak Sin was the governor of Tak Province known as Phya Tak. He and his men were drafted to help in the defense of Ayutthaya, which was facing the full blast of the Burmese siege. Due to his courage and skill in fighting the enemy, he was promoted to be the governor of Kampaeng Phet. But he was popularly referred to as Phya Tak Sin. After the fall of Ayutthaya in 1767, King Tak Sin drove out the Burmese invaders and united Thailand. He started his work of liberation with only five hundred followers, and spent fifteen years in military operations to regain the independence of Thailand. 

Since Ayutthaya had been so completely devastated, King Tak Sin chose to establish his capital at Thonburi (across the river from Bangkok). Thonburi, although a small town, was strategically situated near the mouth of the Chao Phraya River and therefore suitable as a seaport. By that time, foreign trade was needed not only as a way to acquire weapons but also to bolster the Thai economy, which had suffered extensively during the war with Burma.

King Tak Sin's greatest achievement was the rallying of the Thai nation during a time of crisis. He was one of the most remarkable men ever to wear the crown of Thailand through his own ability. At the time of his coronation, he was only thirty-four years of age. He was also interested in promoting a cultural revival in literature and the arts. He was deeply religious and studied meditation to an advanced level. His kindness and bravery as the liberator of Thailand will always be on the Thai people's mind. His achievements have caused posterity to bestow on him the epithet "the Great".