Wei was born to a poor family in 580, shortly before the founding of Sui Dynasty in 581. His family was from Julu Commandery (roughly modern Xingtai, Hebei).
Wei Zheng joined Li Mi's rebellion against Sui Dynasty during his youth.
Wei lost his father early in life and was poor, but had great expectations, not caring about making wealth. At one point, he became a Taoist monk. He favored studying, and as he saw that the rule of Emperor Yang of Sui was beginning to make Sui fall into a state of confusion, he particularly paid attention to strategic works.
Wei Zheng had great ambitions. He joined Li Mi in his rebellion and followed him to the tang territiry. Wei Zheng was captured by Dou Jiande and became the chief imperial chronicler. After Dou Jiande passed away, Wei Zheng was invited to serve as librarian by Emperor Gaozu's oldest son Li Jiancheng, the crown prince. When Li Shimin became Emperor after the Xuanwu Gate incident, he promoted Wei Zheng to an advisor in the imperial administration. Wei Zheng had the fortitude to speak up on all matters. He delibarated state affairs with Emperor Taizong and gave his comments and recommendations as needed. All his suggestions showed his belief in "preparing for danger during times of safety, honouring frugality and suppressing extravagance".
Wei Zheng aired his opinions before Emperor Taizong 50 times and wrote 11 petitions. He offered a countless admonotions with great determination, more than anone else in Chinese history.
After Wei Zheng's death in AD 643 Emperor Taizong was grief-stricken and said sadly: "Using copper as a mirror allows one to keep his clothes neat. Using history as a mirror allows one to see the future trends. Using a person as a mirror allows one to see what is right and what is wrong. When Wei Zheng died, I lost a mirror"
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