Li Yi was born in 810, at Daming Palace, as the thirteenth of twenty known sons of then-reigning Emperor Xianzong.
His mother was Emperor Xianzong's concubine Consort Zheng, who had previously been a concubine of the warlord Li Qi and who, after imperial forces defeated Li Qi in 807, was taken into Emperor Xianzong's palace to be a servant girl to Emperor Xianzong's wife Consort Guo, but who at some point bore Li Yi for Emperor Xianzong.
Consort Zheng is not known to have borne any other children for Emperor Xianzong.
After Emperor Xianzong died in 820, Li Yi's older brother Li Heng, born of Consort Guo, became emperor (as Emperor Muzong), and in 821, when Emperor Muzong created a number of his sons and brothers to be imperial princes, Li Yi was created the Prince of Guang.
In Li Yi's youth, he was said to be shy and a poor speaker, even though he was actually intelligent.
Because of his shyness and difficulty in speaking, he was considered by others to be unintelligent.
Later, during the reigns of Emperor Muzong's sons Emperor Wenzong and Emperor Wuzong, Li Yi was said to try to hide himself from the political scene, and he rarely spoke anything at all.
When the emperors would visit the imperial princes' residences, known as the Sixteen Mansions, they would, as a game, try to get Li Yi to speak, and they referred to him as "Uncle Guang."
It was said that Emperor Wuzong, who had an outgoing personality, particularly disrespected Li Yi.
In early 846, Emperor Wuzong becomes extremely ill and unable to speak.
The palace eunuchs gather and decide on Li Yi as Emperor Wuzong's successor, probably because they consider him unintelligent and therefore easier to control.
They have an edict issued in Emperor Wuzong's name creating Li Yi crown prince and changing his name to Li Chen and putting him in charge of the imperial affairs.
It is said that only when Li Chen met the officials in his role as crown prince that his appropriate expressions of sadness and actions on pending matters caused people to begin to see that he was truly intelligent.
Soon, Emperor Wuzong dies, and Li Chen takes the throne as Emperor Xuānzong.
Emperor Xuānzong honorshis mother Consort Zheng as empress dowager.
Immediately after taking the throne, Emperor Xuānzong acts against the powerful chancellor Li Deyu, who had dominated the court during Emperor Wuzong's reign, as he despises Li Deyu for monopolizing power.
Emperor Xuānzong removes Li Deyu from his chancellor position and sends him from he capital to serve as the military governor of Jingnan Circuit (eadquartered in modern Jingzhou, Hubei); he also remove Li Deyu's fellow chancellor Zheng Su.
