He was also called "Ducal Grandson" Gongsun Qi 公孫起 because he was related to the house of Qin. Bai Qi was appointed to the position of Right Militia General (you shuzhang 右庶長) after he had been recommended to King Zhaoxiang 秦昭襄王 (r. 306-251) by Counsellor-in-chief Wei Ran 魏冉, and was granted the twelfth grade of nobility (zuogeng 左更).
In 293 he defeated the armies of Han 韓 and Wei 魏 at Qique 伊闕 (modern Longmen 龍門 southeast of Luoyang) where he had 240,000 troops of the enemy massacred. For this victory he was promoted to Defendor-in-chief (guowei 國尉), and shortly after to supreme commander (daliangzao 大良造). In 278 he attacked the state of Chu 楚 and was able to conquer the city of Yan 鄢, a year later he took the capital of Chu, Ying 郢. King Zhaoxiang thereupon enfeoffed him as Lord of Wu'an 武安君.
In 272 his troops defeated the joint armies of Zhao 趙 and Wei at Huayang 華陽 (south of modern Zhengzhou 鄭州, Henan), where he again had massacred submitting soldiers, this time numbering 150,000. He ordered a third large massacre of submitting soldiers in 259 after the battle of Changping 長平 (northwest of modern Gaoping 高平, Shanxi) where he had defeated the army of Zhao, this time burying alive more than 400,000 troops.
After this battle he suggested leading the Qin army directly into the heart of Zhao to destroy that state. But at the court Fan Ju 范雎, envious of Bai Qi's successes, persuaded the king to adopt a softer stance. Zhao had to cede territory and was forced to demobilize its army. Two years later the army of Qin suffered defeat during the siege of Handan 邯鄲, the capital of Zhao. Bai Qi, who felt hurt because of Fan Ju's intervention at the court, refused to take over the siege. If the former victory had been used directly to destroy Zhao, he argued, the actual defeat would not have been possible. He feigned sickness instead of offering his serve.
Fan Ju, highly estimated by the king at that time, suggested demoting Bai Qi to a common soldier and to summon him to the court. On his way to the capital Bai Qi committed suicide at Duyou 杜郵.