In 1760, Alaungpaya of Burma led his armies invading Ayutthaya. Uthumphon was asked to leave monkhood to fight against the Burmese. However, Alaungpaya died during the campaigns and the invasion suspended. Uthumphon, once again, returned to monkhood.
The Burmese, however, came back in 1767 under the commission of Hsinbyushin and led by Ne Myo Thihapate. Ayutthaya under Ekkathat was in turmoil, without authorities or powers to counter the Burmese invaders. Though he was strongly urged to take role in leading Siamese armies, Uthumphon chose to stay in the monk status. Ayutthaya finally fell. Uthumphon was captured by the Burmese forces and was brought to Burma along with a large number of Ayutthaya's people.