He was the second emperor of the Tang Dynasty of China, ruling from 626 to 649. As he encouraged his father, Li Yuan (later Emperor Gaozu) to rise against Sui Dynasty rule at Taiyuan in 617 and subsequently defeated several of his most important rivals, he was ceremonially regarded as a co-founder of the dynasty along with Emperor Gaozu.

He is typically considered one of the greatest in Chinese history. Throughout the rest of Chinese history, Emperor Taizong's reign was regarded as the exemplary model against which all other emperors were measured, and his "Reign of Zhenguan" was considered a golden age of Chinese history and required study for future crown princes. During his reign, Tang China flourished economically and militarily. For more than a century after his death, Tang China enjoyed peace and prosperity. During Taizong's reign, Tang was the largest and the strongest nation in the world. It covered most of the territory of present-day China, Vietnam, Mongolia and much of Central Asia until east Kazakhstan. It laid the foundation for Xuanzong's reign, which is considered Tang China's greatest era.