He was made Prince Yidu (宜都王) in Year Wude 3, Prince Wei (衛王) the next year, and made Prince Wei (魏王) in Zhenguan 2, and Prince Bu (濮王) in Zhenguan 21. He was also named Prince of Donglai District (東萊郡王) and Prince Shunyang (順陽王).
After his elder brother Crown Prince Li Chengqian fell out of favour with Taizong, Tai was given the position of Governor of Xiang Commandry (相州都督 Xiangzhou Dudu). However, Tai refused the position and stayed in the capital. Taizong commanded the establishment of a scholar academy in the prince's residence and increased his salary over that of his elder brother. Moreover, Taizong invited Tai to move into Dewu Hall (武德殿) of the imperial palace. Most officials were against these acts.
Li Tai was made the new crown prince after his brother tried to rebel. However, after being made the crown prince, Li Tai tried to hurt Li Chengqian numerous times and exhibited an overwhelming vicious ambition. So Taizong replaced Li Tai with the more popular "virtuous" Li Zhi as the next crown prince. Li Zhi became Emperor Gaozong of Tang China.
The Buddhist statues in the Main Wall of Bingyang South Cave (賓陽南洞正壁) of the Longmen Caves was dedicated by Li Tai to his deceased mother, Gongsun-shi.