The evidence in Fernão Mendes Pinto's record states that he was the natural brother of King Chairachathirat.

Chairacha died in 1546 and his son, Prince Kaewfa succeeded to the throne as King Yodfa, with his mother Sisudachan as regent.

Before doing so however, Thianracha was her co-regent, but wishing to remain faithful to his wife Sri Suriyothai, he became a monk to the Queen Mother's amorous advances.

[2]: 38 "A band of brothers", retired officers, led by Khun Piren staged a counter-coup, killing Worawongsathirat and Si Suda Chan.

(Maha Chakkraphat passed over tradition by elevating Phiren Thorathep instead of one of his sons; but he, when still Prince Thianracha, had himself never been titular ruler of Phitsanulok.)

Upon Maha Chakkraphat's ascension, King Tabinshweti of the Burmese Dynasty of Toungoo marched to Ayutthaya, trying to take advantage of the upheavals in the Siamese capital.

The mission worked, the Burmese armies retreated but later they ambushed at Kamphaeng Phet the Siamese troops led by Prince Ramesuan and Maha Thammarachathirat.

[3]: 20–21 After the war of 1548, Maha Chakkraphat insisted on battling Burmese armies near Ayutthaya, so he heavily fortified the city and de-fortified three nearby cities, Suphanburi, Lopburi and Nakhon Nayok in order to prevent the Burmese from taking them as bases.

The Burmese army then reached Ayutthaya and laid siege, bombarding the city so immensely that Maha Chakkraphat "agreed to come to friendly relations with His Majesty of Hongsawadi."

[4] Though Damrong Rajanubhab asserts the king only entered the monastery after his daughter Phra Thepkasattri was kidnapped by the Burmese, giving up his throne in dishonor.