Cen Xi's grandfather Cen Wenben served as a during the reign of , and his father Cen Manqian served as the secretary general of the capital prefecture Yong Prefecture and carried the title of Duke of Xi.
Cen Xi himself passed the imperial examinations sometime before 691 and served as ''Taichang Boshi'' , an official at the ministry of worship. In 691, during the reign of Emperor Taizong's daughter-in-law Wu Zetian, who had declared a new Zhou Dynasty and interrupted Tang Dynasty, Cen Xi's uncle Cen Changqian, then a chancellor, was accused of treason and executed. As a result, Cen Xi was demoted to be a legal officer at Chen Prefecture . He was subsequently made the magistrate of Jintan County. At that time, his brother Cen Zhongxiang was the magistrate of nearby Changzhou County and another brother Cen Zhongxiu was the magistrate of Lishui County . All three were known for their abilities in governance. The chancellor Zong Chuke, when an official was sent to examine the governance of the circuit containing those three counties, made the comment, "Do not forget about the three Cens east of the Yangtze River." He subsequently recommended Cen Xi, and Cen Xi was made the magistrate of Sishui County, near the capital Luoyang -- which was considered a major promotion due to its location.
As of 704, Cen Xi was serving as the magistrate of Guangwu County , when Wu Zetian asked the chancellors to recommend officials suitable of serving as low level officials in various ministries. The chancellor Wei Sili recommended Cen, but commented, "Alas, his uncle was Cen Changqian, and he suffers from the taint." Wu Zetian responded, "As long as he is capable, what taint can there be?" She therefore made Cen ''Tianguan Yuanwailang'' , an official at the ministry of civil service affairs. It was said that based on Cen's precedent, thereafter family members of officials previously killed during Wu Zetian's reign were able to begin getting promoted.
During Emperor Zhongzong's second reign
In 705, Wu Zetian was overthrown in a coup led by Zhang Jianzhi, Cui Xuanwei, Huan Yanfan, Jing Hui, and Yuan Shuji, and her son and crown prince , a former emperor, was restored to the throne . However, Wu Zetian's nephew Wu Sansi the Prince of Liang soon became a lover of Emperor Zhongzong's powerful wife and a trusted advisor of Emperor Zhongzong's. When the five coup leaders subsequently wanted to submit a petition to Emperor Zhongzong to have the ranks of Wu Sansi and other Wu clan members reduced, initially, no one was daring to draft the petition for them, but Cen Xi, then serving as ''Zhongshu Sheren'' , a mid-level official at the legislative bureau of government , was willing to do so, and wrote an eloquent argument for the proposal. Later that year, after Wu Sansi was successful in having the five coup leaders removed from government, he had Cen made ''Mishu Shaojian'' , the deputy director of the archival bureau -- an ostensibly honored position that carried little actual power. Eventually, he was made a deputy minister of civil service affairs and was in charge of selecting officials, along with Cui Shi, Zheng Yin, and Li Yuangong . Cui, Zheng, and Li were all known for corruption, but Cen was known for his integrity, during this time. Meanwhile, according to historical records that Cen himself later compiled, around this time, when Emperor Zhongzong's brother the Prince of Xiang and sister Princess Taiping were implicated in a failed coup by Emperor Zhongzong's son and crown prince Li Chongjun in 707 in which Wu Sansi and his son Wu Chongxun were killed, Cen and Xiao Zhizhong were the two officials who spoke on Li Dan's behalf, prompting Emperor Zhongzong to stop the investigation against Li Dan.
During Emperor Shang's reign and Emperor Ruizong's second reign
In 710, Emperor Zhongzong died suddenly -- a death that traditional historians believed to be a poisoning by Empress Wei and her daughter Li Guo'er the Princess Anle, so that Empress Wei could become "emperor" like Wu Zetian and LI Guo'er could be crown princess. Soon thereafter, before Emperor Zhongzong's death was announced, Empress Wei, as part of the governmental reorganization to consolidate her power, gave Cen Xi the designation ''Tong Zhongshu Menxia Pingzhangshi'' , making him a chancellor ''de facto''. For the time being, Emperor Zhongzong's son by a concubine, the Prince of Wen, was named emperor , but Empress Wei retained power as empress dowager and regent. She sent a number of officials to survey the circuits, and Cen was sent to survey the Henan Circuit .
Less than a month later, Princess Taiping and Li Dan's son the Prince of Linzi rose in rebellion and killed Empress Dowager Wei and Li Guo'er. Under their support, Li Dan, himself a former emperor, returned to the throne , displacing Emperor Shang. Cen was made ''You Sanqi Changshi'' and minister of justice , and later demoted to be the prefect of Shan Prefecture . He was, however, soon recalled to be the minister of census . In 712, he was made chancellor ''de facto'' again, with the greater designation of ''Tong Zhongshu Menxia Sanpin'' . He was put in charge of editing the imperial history and also the register of clans. In editing the chronicles of Emperor Zhongzong's reign, he recorded how he and Xiao Zhizhong had spoken in Emperor Ruizong's defense when Li Chongjun's coup attempt occurred, and when Emperor Ruizong read the records, Emperor Ruizong thanked Cen and awarded him with silk and a good horse; Emperor Ruizong also made him ''Shizhong'' , the head of the examination bureau , a post considered one for a chancellor. Emperor Ruizong also created him the Duke of Nanyang.
At that time, Cen Xi's older brother Cen Xian was the deputy principal of the imperial university, and his younger brothers Cen Zhongxiang and Cen Zhongxiu were prefectural prefects. Some 10s of his clan members were in fairly important positions. Cen Xi, at one point, sighed and commented, "When things become extreme, they will be reversed. This is what I am fearful of." However, he did not actually resign.
During Emperor Xuanzong's reign
In 712, Emperor Ruizong passed the throne to Li Longji, who was then crown prince, and Li Longji took the throne as Emperor Xuanzong. At the suggestion of Princess Taiping, however, Emperor Ruizong retained power as ''Taishang Huang'' , and Princess Taiping continued to be influential through Emperor Ruizong. Cen Xi was considered a member of her party. Later in 712, Emperor Xuanzong's associates, the chancellor Liu Youqiu and the general Zhang Wei , with Emperor Xuanzong's approval, planned to kill Cen and two other chancellors aligned with Princess Taiping -- Dou Huaizhen and Cui Shi -- but the news was leaked after Zhang informed the plan to the official Deng Guangbin . Liu, Zhang, and Deng were spared but exiled.
By 713, it was said that Princess Taiping, Dou, Cen, Xiao Zhizhong, Cui; along with other officials Xue Ji, Li Jin the Prince of Xinxing , Li You , Jia Yingfu , Tang Jun ; the generals Chang Yuankai , Li Ci , and Li Qin ; and the monk Huifan , were plotting to overthrow Emperor Xuanzong. It was further said that they discussed, with the lady in waiting Lady Yuan to poison an aphrodisiac that Emperor Xuanzong took regularly known as ''chijian'' ). When this alleged plot was reported to Emperor Xuanzong by Wei Zhigu, Emperor Xuanzong, who had already received advice from Wang Ju , Zhang Shuo, and Cui Riyong to act first, did so. He convened a meeting with his brothers Li Fan the Prince of Qi, Li Ye the Prince of Xue, Guo Yuanzhen, along with a number of his associates — the general Wang Maozhong , the officials Jiang Jiao and Li Lingwen , his brother-in-law Wang Shouyi , the eunuch Gao Lishi, and the military officer Li Shoude — and decided to act first. On July 29, Emperor Xuanzong had Wang Maozhong take 300 soldiers to the imperial guard camp to behead Chang and Li Ci. Then, Jia, Li You, Xiao, and Cen were arrested and executed as well. After his death, Cen's properties were confiscated.