After Dezong's grandson Xianzong ascended the throne, Wu became a chancellor and later served with distinction as governor of Xichuan Circuit in modern Chengdu, where he was a patron of the eminent poet Xue Tao.
His family was from Henan Municipality (河南, i.e., the region of the Tang dynasty eastern capital Luoyang).
However, Emperor Dezong knew of his abilities and recalled him to serve as Bibu Yuanwailang (比部員外郎), a low-level official at the ministry of rites (禮部, Libu).
After about a year, he was promoted to be Zuosi Langzhong (左司郎中), one of the chief secretaries at the executive bureau of government (尚書省, Shangshu Sheng).
[9] Almost immediately thereafter, Emperor Xianzong was faced with the situation where Li Qi the military governor of Zhenhai Circuit (鎮海, headquartered in modern Zhenjiang, Jiangsu), who had initially offered to come to the capital to pay homage to him, instead requested a deferral.
How can Your Imperial Majesty expect to command the empire?Emperor Xianzong agreed and issued an edict summoning Li Qi.
Li Qi, receiving the edict, panicked and rebelled, and was soon captured by his own subordinates, delivered to Chang'an, and executed.
Later that year, when the general Gao Chongwen, who had in 806 become the military governor of Xichuan Circuit (西川, headquartered in modern Chengdu, Sichuan), offered to resign his position to be moved to a border circuit, Emperor Xianzong looked for an appropriate replacement for Gao but was unable to find one quickly, and so made Wu the military governor of Xichuan, still carrying chancellor title as an honorary title.
[10] Meanwhile, Wu Yuanji's allies Wang Chengzong the military governor of Chengde Circuit (成德, headquartered in modern Shijiazhuang, Hebei) and Li Shidao the military governor of Pinglu Circuit (平盧, headquartered in modern Tai'an, Shandong), were repeatedly pleading on Wu Yuanji's behalf for an imperial pardon, but Emperor Xianzong refused their requests.
The assassins sent letters to the imperial guards and the governments of Jingzhao Municipality (京兆, i.e., the Chang'an region) and the counties, threatening to kill anyone who dared to pursue them, and it was said that the officials thus did not hunt for them diligently, despite Emperor Xianzong's stern orders.
Emperor Xianzong had Zhang and the others arrested and interrogated by the mayor of Jingzhao, Pei Wu (裴武), and the imperial censor Chen Zhongshi (陳中師).
[10] Emperor Xianzong declared a five-day mourning period for Wu Yuanheng and gave him great posthumous honors.