Nothing is known about Xu Yuanlang's background other than that he was from Yan Province (兗州, roughly modern Jining, Shandong).
In spring 618, after another major rebel leader, Li Mi the Duke of Wei, achieved a great victory over the Sui general Wang Shichong and approached the Sui eastern capital Luoyang, Xu Yuanlang, along with several other key rebel leaders, nominally submitted to him and requested that he take imperial title, but Li declined.
In 621, when Zheng was under attack by the Tang general Li Shimin (the eventual Emperor Taizong), Dou requisitioned troops from Xu to aid Wang.
Xu then submitted to Tang as well and was made the commandant of Yan Prefecture and again created the Duke of Lu.
During the next year, various people in the locale vacillated in their allegiance to Xu's Lu state and Tang.