He originated from Langya 琅琊 (modern Jimo 即墨, Shandong) and studied the Confucian Classics in his young years. He was promoted to court gentleman (lang 郎) and then to magistrate (ling 令) of Yunyang 雲陽. Because of his good reputation he was made Commandant-in-ordinary (zhongwei 中尉) of the Prince of Changyi 昌邑, Liu He 劉賀.
Wang Ji several times remonstrated against the Prince who rather liked going to hunt than to care for his territory, but the Prince did not care. When Emperor Zhao 漢昭帝 (r. 87-74 BCE) died, Liu He was made emperor, but because of his irresponsible behaviour, he was demoted by the regents after less than one month of reign. His former officials were all put into jail, among them also Wang Ji. He was the only person was who was spared execution and was instead sentenced to hard labour.
Yet under the reign of Emperor Xuan 漢宣帝 (r. 74-49 BCE), he was released and appointed regional inspector (cishi 刺史) of the province of Yizhou 益州 (modern Sichuan), but he soon withdrew from office because of illness. Later on he was appointed Confucian erudite (boshi 博士) and Grand master of remonstrance (jian dafu 諫大夫).
Emperor Xuan suffered under the dominance of the kinsmen of the empresses (waiqi 外戚), the families Xu 許, Shi 史 and Wang 王. On the other side, he neglected the memorials of responsible ministers like Wang Ji or Gong Yu 貢禹 who stressed that the general style of the central government had to change and to care for a more benevolent and rational style in the Confucian sense. Wang Ji was very disappointed about the emperors carelessness and retired from office.
When Emperor Yuan 漢元帝 (r. 49-33 BCE) mounted the throne, he was invited for an audience, but died on the way to the capital.