He hailed from Puyang 濮陽 (modern Puyang, Henan) and was a so-called wandering knight (youxia 遊俠) in his early years offering his service to anyone who could use him. During the reign of Emperor Jing 漢景帝 (r. 157-141 BCE) he became a frontrider (xianma 洗馬, sic!) of the crown prince and was even promoted to governor (taishou> 太守) of the commandery Donghai 東海 under Emperor Wu 漢武帝 (r. 141-87 BCE).
His administration was smooth and friendly and contributed to the popularity of the dynasty in his commandery. He was therefore appointed Commandant of the nobles (zhujue duwei 主爵都尉).
Ji An was an adherent of the Huang-Lao school of thought 黃老 and submitted several memorials to Emperor Wu to rule in a benevolent and quiet manner. He consequently contradicted the new policy towards the steppe federation of the Xiongnu 匈奴 and advocated peace with them instead of war. He was later transferred to the post of governor of Huaiyang 淮陽, where he died in office.