Niu Sengru
It is not known when Li Zongmin was born. His great-great-grandfather was Li Yuanyi () the Prince of Zheng, a son of Tang Dynasty's founding emperor Emperor Gaozu. His great-grandfather was Li Jing (), who inherited the Prince of Zheng title from Li Yuanyi. His grandfather Li Chayan () was not listed with any offices while alive but was listed with a posthumous honor, while his father served as a supervisory official at the imperial government and as a prefectural prefect, and also carried the title of Duke of Chenliu. Li Zongmin's cousin Li Yijian served as a chancellor during the reign of Emperor Xianzong. Li Zongmin himself passed the imperial examinations in the "Jinshi" class in 805, during the reign of Emperor Xianzong's grandfather Emperor Dezong, in the same year as eventual colleague and ally Niu Sengru.