Du Ruhui
In 629, Dai became the minister of census, as well as an advisor to Emperor Taizong's son and crown prince Li Chengqian. In 630, while the chancellor Du Ruhui was on his deathbed, he submitted a suggestion to Emperor Taizong that Dai be put in charge of civil service affairs, and Emperor Taizong therefore had Dai, in addition to his other responsibilities, also become the minister of civil service affairs—and also gave Dai the additional designation of "Canyu Chaozheng" (), making him a "de facto" chancellor. It was said that Dai was capable, but as he was not learned, he selected largely people who are capable in the law and not in writing, and was criticized by others at the time for this. Later in the year, he was no longer the minister of civil service affairs, but he kept his other posts and continued to be designated "de facto" chancellor. He was also created a duke.