After he passed the imperial examinations, he became a military officer at Wu Prefecture (婺州, roughly modern Jinhua, Zhejiang).
At that time, the official Yang Fu (楊孚) was serving as the military advisor to the prefect of Hua Prefecture (華州, roughly modern Weinan), which Zheng County belonged to, and was impressed with Du.
Du later served as imperial attendant (給事中, Jishizhong), but later left civil service to observe a mourning period when his stepmother died.
In 724, then-Protectorate General to Pacify the West, Zhang Xiaosong (張孝嵩), was made the mayor of Taiyuan Municipality, and he recommended Du to replace him.
It was said that during Du's service as protectorate general, he cared greatly for the soldiers under him and worked hard, earning the love of both the Han Chinese and the non-Han.
This drew Emperor Xuanzong's displeasure with them, and he removed all three of them, replacing them with Yuwen Rong and Pei Guangting, while retaining fellow chancellor Xiao Song.
He later successively served as prefect of Wei Prefecture (魏州, in modern Handan, Hebei) and mayor of Taiyuan Municipality.
In Emperor Xuanzong's absence, Du conscripted soldiers to repair the three main palaces and the city walls, personally attending to the projects without rest.
Later, Du was made the minister of rites (禮部尚書, Libu Shangshu) and created the Marquess of Wei County.
There was a dispute over his posthumous name, as the ministry of worship initially suggested Zhensu (貞肅, meaning "faithful and stern"), while the officials Liu Tongsheng (劉同升) and Wei Lian (韋廉) believed that Du was both faithful to the state and filially pious and should be given a greater posthumous name signifying both virtues.