It is not known when Zheng Yanchang was born. His family was part of the Zheng clan known as the "Northern Ancestor" branch and traced its line from the ruling house of the Spring and Autumn period state Zheng; its ancestors also included officials of Han Dynasty, Cao Wei, Jin Dynasty, Later Zhao, Former Yan and/or Later Yan, Northern Wei, Northern Zhou, and Tang Dynasty. Of Zheng Yanchang's closer relatives was his third cousinZheng Congdang, who was a chancellor during the reign of Emperor Xizong. However, Zheng Yanchang's own immediate ancestors did not appear to be particularly prominent—as his great-grandfather Zheng Shen was a county sheriff and his grandfather Zheng Zezhi was an imperial guard officer, although his father Zheng Yi was a prefectural prefect. He had at least one older brother, Zheng Yunsheng, and one younger brother, Zheng Yanji. Zheng Yanchang passed the imperial examinations late in the Jinshi class late in the Xiantong era of Emperor Xizong's father Emperor Yizong. He later became an imperial censor with the title Jiancha Yushi.
When the former chancellor Zheng Tian became the military governor of Fengxiang Circuit during the reign of Emperor Xizong, probably in 879, he invited Zheng Yanchang to serve on his staff. After the major agrarian rebel Huang Chao attacked the imperial capitalChang'an in 880, forcing Emperor Xizong to flee to Chengdu, Emperor Xizong left Zheng Tian in command of the remaining Tang forces in the capital region. Zheng Tian put Zheng Yanchang in charge of the logistics of supplying the soldiers with food, as well as issuing orders to the armies to comfort them. After Zheng Tian later joined Emperor Xizong's administration-in-flight at Chengdu as chancellor again, in 882, Zheng Tian had Zheng Yanchang made Sixun Yuanwailang, a low-level official at the ministry of civil service affairs, as well as an imperial scholar. Later, Zheng Yanchang was made the deputy minister of defense, the mayor of Jingzhao Municipality, and the acting director of finances.
Chancellorship and after chancellorship
In 892, by which time Emperor Xizong had died and been succeeded by his brother Emperor Zhaozong, Zheng Yanchang, who was then the minister of census, was made Zhongshu Shilang, the deputy head of the legislative bureau of government, and a chancellor with the designation Tong Zhongshu Menxia Pingzhangshi. He was then also made the minister of justice. His service as chancellor was said to be undistinguished. In 893, when the warlordLi Maozhen the military governor of Fengxiang tried to foster protests at Chang'an against Emperor Zhaozong's planned campaign against him, the protest crowd surrounded Zheng and fellow chancellor Cui Zhaowei on one occasion and attacked them, forcing them to take refuge in people's houses. In 894, Zheng was removed from his chancellorship and made You Pushe, one of the heads of the executive bureau, as he was ill. He subsequently died—with his biography in the New Book of Tang implying that the death was shortly after his removal, but giving no dates.
