He hailed from Kaifeng 開封 (modern Kaifeng, Henan) and was an expert in the old-text classics (guwenjing 古文經) and opponent of the apocryphal classics (chenwei 讖緯) that enjoyed great popularity at that time. He was especially interested in the Gongyang Commentary 公羊傳 and the Zuozhuan Commentary 左傳 to the Chunqiu 春秋 "Spring and Autumn Annals".
When Liu Xuan 劉玄 proclaimed himself emperor, Zheng Xing was appointed aide (zhangshi 長史) to the Counsellor-in-chief (chengxiang 丞相) Li Song 李松 and suggested to the Gengshi Emperor 更始帝 (r. 23-25 CE, i.e. Liu Xuan) to move his seat of government to Chang'an 長安 (modern Xi'an 西安, Shaanxi), the old capital of the Han dynasty. When the army of the Red Eyebrow rebels 赤眉 entered the metropolitan region, Zheng Xing withdrew to the western region that was under the control of Wei Ao 隗, formally appointed regional inspector (cishi 刺史) of Liangzhou 涼州.
In 30 CE, when Liu Xiu 劉秀 founded the Later Han dynasty, he returned to the east and was appointed Senior grand master of the palace (taizhong dafu 太中大夫), a position he used to support the government of the Emperor Guangwu 漢光武帝 (r. 25-57 CE., i.e. Liu Xiu) with useful advice. In 33 CE Zheng Xing participated in Wu Hanju's 吳漢俱 campaign against Gongsun Shu 公孫述 who controlled the region of Sichuan. When Gongsun Shu was defeated, Zheng Xing was ordered to head the military occupation of that region.
Not long after he was accused of secretly buying slaves and was dismissed. Zheng Xing spent the rest of his life as a private teacher.