He was a son of King Wuling 趙武靈王 (r. 325-299) and brother of king Huiwen 趙惠文王 (r. 298-266), to whom and whose successor, King Xiaocheng 趙孝成王 (r. 265-245), he served as Counsellor-in-chief. Zhao Sheng was fond of wandering philosophers, disputers and worthies of all kinds, and assembled several thousand of them at his court.
He was first made governor (taishou 太守) of Dongwu 東武. After the disastrous battle of Changping 長平, the army of Qin 秦 besieged the capital of Zhao, Handan 邯鄲. In this situation Zhao Sheng used all his fortune to bring relief for the refugees and to assemble a new army that was able to withstand the army of Qin for three years. Only then he looked for help from the state of Wei 魏. A joint army of Wei and Chu 楚 was able to liberate Handan. In later years Zhao Sheng was given the title of Lord of Pingyuan.