Hnaung was initially a loyal vassal of his father King Nanda until 1594 when he openly clashed with his brother Crown Prince Minye Kyawswa.
His attempts to take over territories beyond Prome's traditional vassals in the present-day Magwe Region were unsuccessful.
The self-proclaimed king was assassinated by Yan Naing, one of his trusted advisers, on the eve of his planned invasion of Upper Burma in 1597.
The future Thado Dhamma Yaza III was the youngest child of Crown Prince Nanda and his chief consort Hanthawaddy Mibaya.
[2][3] Hnaung became the third in line of succession behind his elder brothers Mingyi Swa, the heir-apparent, and Minye Kyawswa.
[6] Nanda appointed Hnaung the next king of Lan Xang although he had reservations about sending his teenage son to the remote rebellion-prone kingdom.
[13] Tired of constant war, able men had fled military service to become monks, indentured servants, private retainers or refugees in the nearby kingdoms.
[14] Hnaung himself became disillusioned when the new Crown Prince Minye Kyawswa frantically set out to raise more men—again mainly from Lower Burma by branding men to facilitate identification, executing deserters, and forcing monks into the army.
When the Siamese army invaded the Upper Tenasserim coast in October/November 1594,[16] Nanda asked his vassals to send troops.
Hnaung laid siege to the city, counting on Minye Thihathu to be occupied or defeated by the Siamese army.
[18] He may have reasoned that Upper Burma, which had not had a viceroy since December 1593 following Nanda's policy of devolution in the north, would be unable to put up a coordinated defense.
(Ava had been administered by Chief Minister Bala Yawda and Military Commissioner Let-Yway-Gyi Myin Hmu.
Thissa (commonly known as Nyaungyan Min) agreed to Nanda's order out of his self-interest for he could not allow anyone else to take over Upper Burma.
In the dry season of 1596–97, the forces led by Nyaungyan and Let-Yway-Gyi Myin Hmu launched an attack on Prome's northernmost possessions.
The northern forces took a heavily fortified Pakhan, the northernmost Prome possession 120 km south of Ava.
After all the fighting was done, depleted Prome forces had fallen back to their next fortified garrison at Salin, 240 km south of Ava.
5 September] 1597, as he was about to set sail with his flotilla to Ava, Thado Dhamma Yaza Mingyi Hnaung was assassinated by one of his trusted advisers, Gov.
Yan Naing's men quickly seized the barge and forced Hnaung, who did not swim, into the river.
Minye Thihathu opportunistically redirected the Toungoo army, which was already in the Ava territory, to attack Prome.
[22][23] (Nyaungyan was forever grateful to Yan Naing for breaking up what would be a two-pronged attack by Prome and Toungoo.
In 1605, as he lay dying, he asked his eldest son and heir-apparent Anaukpetlun to spare the life of Yan Naing when Prome was captured.
When asked why, the king replied that if Yan Naing had not broken up the invasion, his then small army would likely have been defeated in a two-front war.