During the late Jin, Xu Xianzhi served as an assistant to the official Wang Ya (王雅), and then to the general Liu Laozhi (劉牢之).
When Emperor Wu grew ill in 422, he entrusted his crown prince Liu Yifu to Xu, Fu, Xie Hui, and Tan Daoji, and soon died.
Liu Yifu succeeded him (as Emperor Shao), and in the mourning period, he had Xu and Fu handle important matters for him.
Xu remained at Jiankang, while Fu went to Liu Yilong's post at Jing Province (荊州, modern Hubei) to welcome him.
(Fu had changed his mind after advice from the official Cai Kuo (蔡廓), but his letter to Xu to try to stop the assassinations arrived too late.)
In 425, Xu and Fu offered to resign, and Emperor Wen approved and began to handle important matters of state himself.
However, Emperor Wen was resentful that Xu, Fu, and Xie had killed his two older brothers, and in late 425 planned to destroy them, particularly at the urging of Wang Hua and the general Kong Ningzi (孔寧子).
He therefore mobilized troops and publicly declared that he was going to attack rival Northern Wei but was privately preparing to arrest Xu and Fu while engaging in a military campaign against Xie.