On the eighth day of the tenth lunar month (October 30) 1226, he forced the former emperor Lý Huệ Tông, who had already abdicated his power, to commit suicide.
These actions were criticized by historian Ngô Sĩ Liên in his Đại Việt sử kí toàn thư as inhumane, though their purpose was to reinforce the reign of Trần Thái Tông.
[12][13] However, the authenticity of this account was challenged by the historian Ngô Sĩ Liên, because a member of the Lý clan was still appointed as general by Trần Anh Tông and there is no mention this event in Phan Phu Tiên's historical record.
[16][17] According to Đại Việt sử kí toàn thư, Thái Tông and his wife, the Empress Chiêu Thánh, did not have their first son for a while, so this situation in the royal family made grand chancellor Trần Thủ Độ worried because he had profited in the same circumstances of the Emperor Lý Huệ Tông to overthrow the Lý dynasty.
After the royal marriage, Thuận Thiên was entitled the new empress of the Trần dynasty while Chiêu Thánh was downgraded to princess.
In the fury of losing his pregnant wife, Trần Liễu rose in revolt against the royal family.Emperor Thái Tông felt awkward about the situation and decided to become a monk in Yên Tử Mountain.
In the beginning, the Đại Việt army suffered several defeats by an overwhelming force which had already conquered vast areas of Asia.
Once there was a person who went to the Emperor to report him about this suspicion, Thái Tông immediately visited Trần Thủ Độ's place with this man and made him tell everything in front of the grand chancellor.
His successful governing was considered by historical books as the main factor that not only led to the stability of Early Trần period but also contributed to the victory of Đại Việt over the first Mongol invasion.
Trần Thủ Độ politely declined the Emperor's request by an answer: "An Quốc is my brother, if he is better than me then I had better retire from the position, but if Your Majesty think that I am better than him, so please not appoint him for grand chancellor.
[25][28] Sometimes, his Machiavellian figure was compared with Dorgon, the powerful general who helped establish the Qing dynasty's rule in China,[29] or Cardinal Mazarin who was chief minister of France for 20 years.
For this reason, it was not until 2008 that a new street in Hanoi was named in honour of Trần Thủ Độ,[30] a decision which is still met with some opposition from public opinion.
[33] In theatre, on the contrary, there were several plays which exploited the controversial role of Trần Thủ Độ in history such as Rừng trúc (Bamboo Forest) by the writer Nguyễn Huy Tưởng or Anh hùng và mỹ nhân (The Hero and the Beauty) by Chu Thơm.