Li Xin 李信, courtesy name Youcheng 有成, was a general of the state of Qin 秦 during the very late Warring States period 戰國 (5th cent.-221 BCE). He hailed from Huaili 槐里 (today's Xingping 興平, Shaanxi). His father Li Yao 李瑤 was governor (taishou 太守) of the commandery of Nanjun 南郡 and was invested as Marquis of Didao 狄道侯.
In 228, Li Xin was made general under the supreme command of Wang Jian 王翦 during the campaign against the state of Zhao 趙. Li Xin marched from Taiyuan 太原 and liaised with Wang Jian to encircle the army of Zhao and closed a ring around the capital of Zhao, Handan 邯鄲 (today in Hebei). The campaign ended with the destruction of Zhao.
Just after this historic victory, the army of Qin marched towards the northeast to attack the capital of Yan 燕, Jicheng 薊城 (today's Beijing). King Xi of Yan 燕王喜 (r. 255-222) and the heir apparent Prince Dan 太子丹 fled to the region of Liaodong 遼東 farther east, but Li Xin defeated the Prince's last army at River Yan 衍水 (Hunhe 渾河, Liaodong), and the King killed Prince Dan.
King Zheng of Qin 秦王政 (the future First Emperor 秦始皇帝, r. 246-210 BCE) then planned to conquer Chu 楚 in the south. In the preparation for the campaign, he asked Li Xin, how many troops would be necessary to bring down Chu. Over-confident after his victories in the northeast, Li was of the opinion that 200,000 troops would be enough, while Wang Jian thought Qin would need no less than 600,000 troops. The king thereupon entrusted Li Xin and Meng Tian 蒙恬 with the campaign, but they were heavily defeated by Chu general Xiang Yan 項燕.
In spite of this defeat, Li Xin received the command over further campaigns in the northeast—albeit in dual command with Wang Ben 王賁—, and was able to capture the kings of Dai 代 (see Zhao) and Qi 齊. For this achievement, he was invested as Marquis of Longxi 隴西侯, a territory in what is today Gansu, where Li Xin resided thereafter.