Wei Daijia himself started his government career service as an officer in the imperial guard corps, and he married a daughter of the renowned general Li Daozong the Prince of Jiangxia (Emperor Taizong's cousin).
Wei and another officer, Xue Rengui, led their troops to try to aid Xin, who was eventually able to fight off the Goguryeo forces.
Around this time, she made Wei Daijia the minister of civil service affairs and acting Sikong (司空, one of the Three Excellencies), putting him in charge of constructing Emperor Gaozong's tomb.
It was said that Wei, because he had a military background, lacked talent for selecting officials, and therefore did not have a good reputation as a minister of civil service affairs.
Later in 685, Empress Dowager Wu commissioned Wei to lead an army to defend against an Eastern Tujue attack—a campaign that lasted until spring 686.
He set out on the campaign and encountered Tufan forces at Yinshijia River (寅識迦河, flowing through Ili Kazakh Autonomous Prefecture, Xinjiang).