In 937, the Wu regent Xu Zhigao had Wu's emperor Yang Pu yield the throne to him, ending Wu and starting a new state of Southern Tang as its emperor. Xu, upon assuming the throne, commissioned Zhang Juyong, as well as Zhang Yanhan and Li Jianxun, chancellors, with the designation Tong Zhongshu Menxia Pingzhangshi.[2]
In 939, Zhang Juyong was apparently among a group of officials who formally proposed that Xu Zhigao assume his birth family name of Li. (Xu Zhigao had used the family name of Xu because he was adopted by Xu Wen, who was his predecessor as regent, as a child.) Xu Zhigao accepted the proposal and took the new name of Li Bian.[1][3] Zhang Juyong was thereafter given the addition title of Zuo Pushe (左僕射, one of the heads of the executive bureau (尚書省, Shangshu Sheng), while continuing to retain the titles of Menxia Shilang and chancellor. It was said that Zhang Juyong was graceful, silent, and moderate, and that, as chancellor, he expressed few of his opinions.[1]
Li Bian died in 943 and was succeeded by his son Li Jing. In 944, Li Jing removed Zhang from his chancellor position and made him the military governor (Jiedushi) of Zhenhai Circuit (鎮海, headquartered in modern Zhenjiang, Jiangsu).[4] Zhang died not long after, and was given posthumous honors, including the title of Duke of Qinghe and the posthumous name of Yi (懿, "benevolent").[1]