As of the end of Baoli era (825-827) of Emperor Xianzong's grandson Emperor Jingzong, Chen was serving as an imperial censor with the title of Shiyushi (侍御史), and serving at the eastern capital Luoyang, when he was made Yubu Yuanwailang (虞部員外郎), a low-level official at the ministry of public works (工部, Gongbu).
In 835, he was made the deputy minister of worship (太常少卿, Taichang Shaoqing), and continued to serve in his capacities as imperial scholar, tutor to Li Yong, and drafter of edicts.
[4] In 837, when Chen Yixing was also serving as the deputy minister of public works (工部侍郎, Gongbu Shilang), he was made a chancellor de facto with the designation Tong Zhongshu Menxia Pingzhangshi (同中書門下平章事), serving alongside Li Shi and Zheng Tan.
[6] After this incident, he continued to frequently, in veiled terms, accuse Yang of stealing imperial authority while discussing issues.
[7] In particular, later in 838, when Yang advocated for the former chancellor Li Zongmin, also considered a Niu Faction leader, who had been exiled, promoted and moved closer to the capital, Chen opposed vehemently, and it was said that from this point on, all policy arguments were complicated by partisan issues, making it difficult for Emperor Wenzong to rule on them.
Li Jue responded, "Your Imperial Majesty had told me previously that an Emperor should select chancellors, not suspect them."
Li Jue, offended, responded, "Chen Yixing is obviously suspecting that there are chancellors who are stealing power from Your Imperial Majesty.
Emperor Wenzong subsequently sent a eunuch to comfort him, and Zheng partially apologized, stating, "Your subject is foolish.
Chen, instead, was made the deputy minister of civil service affairs (吏部侍郎, Libu Shilang).
[2][6] Later that year, there was an incident in which Emperor Wuzong, believing that Yang Sifu and Li Jue, whom he had stripped of chancellor posts and sent out of Chang'an because he believed that they did not support him as emperor, became further incensed by the powerful eunuch Qiu Shiliang against Yang and Li Jue, as well as two eunuchs trusted by Emperor Wenzong — Liu Hongyi (劉弘逸) and Xue Jileng (薛季稜) — that he ordered Liu and Xue to commit suicide, and further sent eunuchs with orders to force Yang and Li Jue to commit suicide as well.
The defender of Tiande, Tian Mou (田牟), suggested that Wamosi's offer be rejected and that Tang forces attack him, along with allied Tuyuhun, Shatuo, and Dangxiang tribes.
Li Deyu opined differently, believing that Wamosi's offer should be accepted and that food should be supplied to the Huigu remnants.