Trần Nhật Duật was born in 1255 as the sixth son of the Emperor Trần Thái Tông. According to "Đại Việt sử kí toàn thư", Trần Nhật Duật was born with four characters "Chiêu Văn đồng tử" ("pupil of Chiêu Văn") in his arm, that's why he was entitled Prince Chiêu Văn (Vietnamese: Chiêu Văn vương) in 1268. Besides the Emperor Trần Thánh Tông, Trần Nhật Duật had two other famous elder brothers, Prince Chiêu Minh (Chiêu Minh vương) Trần Quang Khải who was grand chancellor of royal court and Prince Chiêu Quốc (Chiêu Quốc vương) Trần Ích Tắc who was broadly known not only for his intelligence but also for his notorious defection to Yuan side during the second Mongol invasion of Đại Việt.