Dou Wei was from Fufeng Commandery (扶風, roughly modern Baoji, Shaanxi).
[2] Dou Wei was considered quiet and studious in his youth, much unlike his brothers and cousins who, as nobles, were far more interested in military matters.
At that time, the government was in a state of flux, and with Dou being knowledgeable with ceremonies and governmental organization, Li Yuan entrusted to him the task of reorganizing the government as well as preparing the ceremonies to have Yang You yield the throne to Li Yuan.
In spring 618, Emperor Yang was killed during a coup at Jiangdu (江都, in modern Yangzhou, Jiangsu) led by the general Yuwen Huaji, and when the news reached Chang'an, Li Yuan had Yang You yield the throne to him, establishing Tang dynasty as its Emperor Gaozu.
He made Dou Wei the head of the legislative bureau (內史令, Neishi Ling), considered one of the posts for a chancellor.