The sixth son of his predecessor, Emperor Duzong, Zhao Xian came to the throne around the age of four, and reigned for less than two years before he was forced to abdicate in 1276.

[citation needed] His sixth son, Zhao Xian, who was then about four years old, was enthroned as the new emperor with assistance from the chancellor Jia Sidao.

[citation needed] By the time Zhao Xian came to the throne, the Mongol-led Yuan dynasty had already taken control of the northern and southwestern areas of China, crossed the Yangtze River and acquired key strategic locations such as Xiangyang.

The Song army suffered defeat and not long afterward, bowing to public pressure, Grand Empress Dowager Xie ordered Jia Sidao's execution.

After the fall of the Song dynasty, Zhao Xian was relocated to the Yuan capital at Dadu (present-day Beijing) then later to Shangdu.

After they crossed the Yangtze River, two former generals, Li Tingzhi (李庭芝) and Miao Zaicheng (苗再成), planned to hijack a transport to carry them all but failed.

Kublai Khan wanted to preserve some vestiges of the Song imperial clan and in October 1288 issued an edict ordering Zhao Xian to relocate to Tibet.

The Khan may have acted out of genuine concern for the former emperor or he may have wished to remove the Song heir to the throne out of China proper.

According to Sakya's monastic succession records, in 1323, the 52-year-old Zhao Xian received an imperial edict ordering him to commit suicide at Hexi (河西; present-day Zhangye, Gansu Province).

The renowned Sinologist Ann Paludan has written, "[His] unexplained suicide in 1323 led to curious rumours, including the suggestion that he was the real father of the future Mongol emperor Shundi [Toghon Temür] (1333–1368), born to a Turkish woman in 1320.

The outbreak of the Song loyalist Red Turban Rebellion in Henan led to a recommendation that Zhao Wanpu should be transferred somewhere else by an Imperial Censor in 1352.

Paul Pelliot and John Andrew Boyle commented on Rashid-al-Din Hamadani's chapter The Successors of Genghis Khan in his work Jami' al-tawarikh, identified references by Rashid al-Din to Zhao Xian in his book where he mentions a Chinese ruler who was an "emir" and son-in-law to the Qan (Khan) after being removed from his throne by the Yuan Empire and he is also called "Monarch of Song", or Suju (宋主 Songzhu) in the book.