He twice led the Hanthawaddy delegation in peace negotiations with Ava in 1391 and in 1430–1431, and secured favorable treaties for his kingdom on both occasions.
Although he is best known as a longtime senior minister, the first mention of Maha Thamun in the royal chronicles is as a commander of a sentinel battalion of the Hanthawaddy army in the first campaign (1385–1386) of the Forty Years' War.
His naval flotilla was instrumental in repulsing the numerically superior Ava invasion fleet, outside the port of Gu-Htut on the Irrawaddy river, in the opening battle of the campaign.
In a famous episode, he advised the king to revoke the royal order to execute the troops that had fled the battle of Nawin (which took place on 26 December 1402).
[13] As the chronicle story goes, Dala had been under siege for months in February 1415 when Commander Emundaya managed to slip through Ava lines to inform the starving forces inside the town that help was on the way, and to hold on for a few more weeks.
[note 5] In his last known command as reported in the chronicles, on 13 March 1415, Maha Thamun led an 800-man regiment in the famous battle outside Dala in which Crown Prince Minye Kyawswa of Ava fell in action.
[16] Ran's main demand was for Thado to acknowledge his 1427 annexation of Tharrawaddy and Paungde, which used to be Ava's southernmost districts.
Thado was so angry at the demand that he reflexively ordered Maha Thamun to be executed; Chief Minister Yazathingyan had to talk him out of it.