In late 895 — during a campaign featuring the imperial government, under Emperor Zhaozong, and Li Keyong the military governor of Hedong Circuit on one side, and Li Maozhen the military governor of Fengxiang Circuit and Wang Xingyu the military governor of Jingnan Circuit on the other — Emperor Zhaozong made Sun Wo, who was then the mayor of Jingzhao Municipality the deputy minister of defense and chancellor with the designation Tong Zhongshu Menxia Pingzhangshi. Later in the year, shortly after a chancellor, Cui Zhaowei, was executed for conspiring with Li Maozhen and Wang. By the end of the year, Li Keyong had defeated Wang, who was then killed by his own subordinates in flight. Li Maozhen and another ally, Han Jian the military governor of Zhenguo Circuit, then outwardly submitted to the imperial government. Emperor Zhaozong therefore ordered Li Keyong to end the campaign and return to Hedong. At some point, Sun was created the Marquess of Le'an. However, by summer 896, the relationship between the imperial government and Li Maozhen had broken down again, and Li Maozhen launched his army to threaten Chang'an. Emperor Zhaozong and the imperial officials decided to flee Chang'an, initially resolving to head to Hedong. However, due to the distance involved and due to Han's avowal of his loyalty, Emperor Zhaozong headed for Han's capital Hua Prefecture instead. While there, he declared a general campaign against Li Maozhen, putting Sun in charge of the campaign and making the general Li Sijian Sun's deputy. However, with Han having a long-time alliance with Li Maozhen, Han interfered with the operation, which, as a result, was never actually launched. By 897, with Han having seized control of the imperial guards that Emperor Zhaozong had previously put several imperial princes in command of, the campaign was cancelled entirely. Soon thereafter, Han falsely accused two close associates of Emperor Zhaozong's — the astronomer Ma Daoyin and the physician Xu Yanshi of crimes and had them executed. With another chancellor, Zhu Pu, being regarded as sheerly incompetent, Han further accused Sun and Zhu of associating with Ma and Xu. As a result, both Sun and Zhu were removed from their chancellor posts, with Sun initially keeping his secondary post as the minister of rites. Later in the year, Sun was demoted and exiled to be the military advisor to the prefect of Nan Prefecture. He died in exile, with the date of his death lost to history. As chancellor, Sun was described to be understanding and frugal. He paid little attention to his outward appearance, once stating, "A gentleman has proper ways to act. One needs not compare his appearance to the appearance to another's; rather, he should act in clear ways so as to contrast with another's murky ways." It was said that whenever he had guests, if his servants had arguments among themselves, he would not rebuke them — stating that if he took time to rebuke them, he would merely be distracting himself.