Xu You was born in , in
Haizhou, China. His father was Xu Zhihui (徐知诲), one of
Xu Wen's five sons. Thus, by default, Xu was already respected for being Xu Wen's grandson. Additionally, many of Xu's relatives worked for the government. During the reign of
Emperor Yuanzong, he became the Grand Guardian of
Li Yu, who was heir apparent to the throne. As Grand Guardian, Xu successfully proposed the construction of a "clear mind pavilion", from which imperial commands would be relayed, on the palace grounds at
Jinling. He was also the chancellor of the capital. After the fall of the Southern Tang dynasty, Xu You was appointed as a
Song court director alongside Xu Xuan (徐铉). Xu is described as a loyal subject of Li Yu. Following the death of Yuanzong in 961, Li Congshan attempted to seize the crown from the heir and his elder brother Li Yu. Viewing this as an opportune moment, the younger Li tried to coerce Xu into passing him Li Jing's final will, citing their shared genealogy and Xu's father's respect for Yuanzong. Xu was not convinced with the unlawful suggestion, however, and promptly reported the matter to the crown prince. Consequently, Li Congshan was demoted from Prince of Han to Duke of Southern Chu. He was a "clever" inventor and reportedly built a working
qiqi (), a time-measuring device, from scratch. By Xu's time, the
qiqi had already been obsolete and virtually none of his peers knew how to operate one. He was also well-read in the arts, especially Chinese painting, and enjoyed travelling, particularly with the royal family. Xu died of an illness. Controversially, Xu Xuan commented on his death, "Would
Zhou Gong and
Confucius play tricks, and cause this man to die an early death?" This insinuated that Xu You was in fact a flawed official who contravened the teachings of the aforementioned sages. ==In popular media==