The cause of the war was an attempt by the Toungoo king Bayinnaung to force the Ayutthaya kingdom into submission under his rule, as part of his campaign that later created the largest empire ever to exist in Southeast Asia.

13 years into Bayinnaung's reign, his second attempt at invasion of Siam and first as king succeeded after an extensive siege of the city of Ayutthaya.

Arms and livestock were taken by the government in preparation for a large-scale war effort, and seven white elephants were captured by Chakkraphat for good luck.

However, after learning that Phitsanulok had fallen, Prince Ramesuan decided to set up camp at Chai Nat to stop the Burmese advance.

Bayinnaung later commanded the Burmese riverine fleet under Thado Dhamma Yaza I of Prome to attack the Siamese.

[7] Bayinnaung was able to capture Lumphli, Jampa, and Ban Dokmai Han Tra Fortresses, surrounding Ayutthaya from three sides.

Although superior in strength, the Burmese were not able to capture Ayutthaya, but demanded that the Siamese king come out of the city under a flag of truce for peace negotiations.

The Ayutthaya Kingdom became a vassal of the Toungoo dynasty, required to give thirty elephants and three hundred catties of silver to the Burmese yearly.

Burmese sources continue to say that after having been sent to Pegu for years, Maha Chakkraphat became a monk and Bayinnaung allowed him to return to Ayutthaya.

[9] Thai sources, however, merely say that Mahinthrathirat, the second son of Maha Chakkraphat, ascended the throne because his father abdicated and became a monk after this war.

[9] Bayinnaung also asked for 4 white elephants alongside Ramesuan, Phraya Chakri and Phra Sunthorn Songkhram as hostages.