Li Zitong was from Donghai Commandery (東海, roughly modern Lianyungang, Jiangsu).
At that time, the agrarian rebel leaders tended to be cruel, but Li was considered kind and tolerant, and therefore many people joined him.
Zuo began to be jealous and suspicious of him, and Li took his men and left in 615, heading south and crossing the Huai River to join another rebel leader, Du Fuwei.
After Emperor Yang was killed in the spring of 618 at Jiangdu (江都, in modern Yangzhou, Jiangsu) in a coup led by the general Yuwen Huaji, Yuwen then left Jiangdu and Li contended for control of the lower Yangtze River region against Du Fuwei, Shen Faxing the King of Liang, and the former Sui general Chen Leng (陳稜).
In 620, Li crossed the Yangtze to attack Shen, who then had his capital at Piling (毗陵, in modern Changzhou, Jiangsu).
Initially, Li Zitong placed his best troops at Dusong Mountain (獨松嶺, in modern Huzhou, Zhejiang), but after Wang pretended to have a much larger army than he actually had, Li Zitong panicked and took up defense at Hangzhou (杭州, also in modern Hangzhou), and was defeated by Wang.
In fall 622, Li Fuwei, concerned that Tang might believe that he was not sufficiently submissive, went to Chang'an to pay homage to Emperor Gaozu.
Emperor Gaozu promoted him in title and granted him the special honor of being seated even above his own son Li Yuanji the Prince of Qi, but did not allow him to return to Danyang.