Around late 209, when the warlord Liu Bei became the Governor of Jing Province, he appointed Pan Jun to serve as an Assistant Officer in the Headquarters Office (). Between 212 and 214, when Liu Bei was away on a campaign to seize control of Yi Province (covering present-day Sichuan and Chongqing) from its governor Liu Zhang, he left Pan Jun behind to assist his general Guan Yu in guarding his territories in Jing Province and overseeing daily affairs.