Maha Chakkraphat (Thai: มหาจักรพรรดิ, pronounced [mā.hǎː t͡ɕàk.krā.pʰát]; 1509 – 1569; Burmese: မဟာချက္ကရဖက်) was king of the Ayutthaya kingdom from 1548 to 1564 and 1568 to 1569. Originally called Prince Thianracha, or Prince Tien, he was put on the throne by Khun Phiren Thorathep and his supporters of the Sukhothai clan, who had staged a coup by killing the usurper King Worawongsathirat and Si Sudachan.

His original name is Thianracha. His initial biography is unclear. Evidence of his family appears in the Royal Chronicles, stating that "he was part of the royal family of King Chairathirat" and in Sangitiyavansa, a Pali text of the Rattanakosin era, stating that he was the nephew of King Chairachathirat. The evidence in Fernão Mendes Pinto's record states that he was the natural brother of King Chairachathirat. Thianracha joined his brother in the campaigns against Lanna and, in 1546, led the siege of Chiang Mai.

Chairacha died in 1546 and his son, Prince Kaewfa succeeded to the throne as King Yodfa, with his mother Sisudachan as regent. She had Yodfa killed in 1548 and eventually put her paramour on the throne as Khun Worawongsathirat. 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.

"A band of brothers", retired officers, led by Khun Piren staged a counter-coup, killing Worawongsathirat and Sisudachan. Phiren Thorathep then elevated Prince Thianracha to the throne as Phra Maha Chakkraphat.

Maha Chakkraphat appointed Phiren Thorathep to the position of King of Phitsanulok as Maha Thammarachathirat, and gave him in marriage his daughter Sawatdirat. (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.) Khun Inthrathep was rewarded with the regency of Nakhon Si Thammarat.

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 Burmese armies stopped near Ayutthaya. Tabinshweti came with his best general, the Uparaja Bayinnaung, Viceroy of Prome and Governor of Bassein. Maha Chakkraphat also took to the battleground his whole family, including Sri Suriyothai, the Uparaja Prince Ramesuan, and Prince Mahinthrathirat. At Pukaothong field, Maha Chakkraphat fought an elephant duel against the Viceroy of Prome but his elephant was overcame and ran away. Sri Suriyothai then rushed to rescue her husband but was slashed to death by the viceroy. The two princes then forced the viceroy to retreat.

The Siamese then put a culverin on a barge and sailed along the Chao Phraya to fire the enemies. The mission worked, the Burmese armies retreated but later they ambushed at Kamphaeng Phet the Siamese troops led by Prince Ramesuan and Maha Thammarachathirat. The Burmese held the two in captivity until Maha Chakkraphat gave up two male war elephants in exchange for his son and Maha Thammarachathirat.