Zheng Xunyu was born in 738, during the reign of Emperor Xuanzong. His family was from Zheng Prefecture. It claimed ancestry from the ducal house of the Spring and Autumn period state Zheng and traced its ancestry through a line of officials of Han Dynasty, Jin Dynasty, Han Zhao or Later Zhao, Former Yan or Later Yan, Northern Wei, Northern Zhou, and Tang Dynasty. His grandfather Zheng Changyu served as a prefectural prefect, while his father Zheng Liang served as a county magistrate. Zheng Xunyu lost his father prematurely. After the Anshi Rebellion erupted in 755, he took his mother into Mount Luhun and supported his mother there, not returning to Zheng Prefecture. After the rebellion was quelled, there were three occasions when the officials Liu Yan and Zhang Xiancheng recommended him to be an official at the county level, and each time he declined the recommendation. During the Dali era of Emperor Xuanzong's grandson Emperor Daizong, Zheng passed the imperial examinations in the special class of those who submitted constructive criticism. He was made Dali Pingshi, a judge at the supreme court. He was later made the secretary general at Yangzhai County, and, after he served with distinction there, was made the sheriff of Wannian County, one of the two counties making up the Tang capital Chang'an.
During Emperor Dezong's reign
After Cui Youfu became chancellor in 779 during the reign of Emperor Daizong's son Emperor Dezong, Cui promoted Zheng Xunyu to be Zuo Bujue, a low-level consultant at the examination bureau of government. He later served as a secretary to the military governor of Jingxuan Circuit, and then returned to Chang'an to serve as an imperial censor with the title Shiyushi then Xingbu Yuanwailang, a low-level official at the ministry of justice. He later left governmental service to observe a mourning period for his mother when she died, and after the mourning period was over, he was moved to the ministry of civil service affairs. Early in Emperor Dezong's Zhenyuan era, he made an order that 10 central government officials be made magistrates of various counties in the Chang'an and Luoyang regions, and Zheng, while retaining his office, was made the magistrate of Fengxian County. The next year, he got promoted to the prefect of Rao Prefecture, and later returned to Chang'an to serve as Jianyi Daifu, a high-level consultant; and then was made the deputy minister of civil service affairs. Later, Zheng was made the mayor of Henan Municipality. Before he could arrive at Henan, there was a birthday for Emperor Dezong, and it was customary for the mayors of the special municipalities to offer horses as tributes. A subordinate of Zheng's requested that he be permitted to fetch a horse to be offered, but Zheng refused, stating, "It is appropriate for someone who has not started serving to offer tributes?" It was also said that Zheng was serious and quiet in his character, and that he did not ask private favors of others; as a result, people did not dare to ask him for private favors. Once he arrived at Henan, he governed the city without much fanfare, and rested the people by lowering taxes and increasing stipends. At that time, the general Han Quanyi was in charge of attacking the rebel general Wu Shaocheng. Henan was responsible for shipping the army's supplies to Han, and Zheng responded by storing food at Yangzhai, reducing the burden of the people in shipping the supplies. Whenever Han and the eunuchs monitoring the army had demands on Henan, Zheng would not agree with those demands unless there were imperial edicts authorizing them. When his subordinates worried for him that this would offend Han and the eunuchs, Zheng responded: Zheng's capability in governing the city was compared to a predecessor, Zhang Yanshang, but he was said to be more serious, lenient, and righteous than Zhang. He was later recalled to serve as deputy minister of civil service affairs again. In 803, he was given the designation Tong Zhongshu Menxia Pingzhangshi, making him a chancellor, along with Gao Ying. At that time, one of Emperor Dezong's close associates, Li Shi the Prince of Dao, was the mayor of Jingzhao Municipality, and Li was well known for being harsh in his tax collections in order to offer tributes to Emperor Dezong. Zheng, disliking the practice, questioned him: At that time, however, Li was trusted by Emperor Dezong, and therefore suffered no ill consequences from Zheng's investigation.
During Emperor Shunzong's and Emperor Xianzong's reigns
In 805, Emperor Dezong died and was succeeded by his son Emperor Shunzong. Emperor Shunzong made Zheng Xunyu the minister of civil service affairs and still a chancellor. At that time, Emperor Shunzong's close associate Wang Shuwen had become very powerful and was allied with Zheng's chancellor colleague Wei Zhiyi. On an occasion, when the chancellors, as per custom, were having lunch together, Wang wanted to see Wei and went to the office of the chancellors to do so. When a guard refused to let Wang in, Wang rebuked the guard and ordered him away. Wei rose from his seat and walked away to confer with Wang. Zheng, and the other chancellors Du You and Gao Ying, stopped dining and waited for Wei to return. After a while, they sent the guard to see what the situation was, and the guard stated, "Wang Shuwen had requested food, and Chancellor Wei is dining with him." Neither Du nor Gao dared to say anything, but Zheng stated, "How can I remain here still?" He had his attendants fetch horses, and he went home and stayed there for seven days, refusing to leave his bed. Several months later, when Emperor Shunzong, then seriously ill, passed the throne to his son Emperor Xianzong, Zheng and Gao were removed as chancellors. Zheng himself died several months later and was given posthumous honors and the posthumous nameWenxian. His sons Zheng Tan and Zheng Lang later served as chancellors during the reigns of Emperor Wenzong and Emperor Xuānzong, respectively.
