As of the reign of Emperor Gaozong's wife Wu Zetian (r. 690–705), Wang Jun served as Dianzhong Shi Yushi (殿中侍御史), a low-level imperial censor and also carried the honorific title of Chaosan Daifu (朝散大夫). On an occasion when the chancellor Wei Yuanzhong was commissioned to defend against an Eastern Tujue incursion, Wei was unable to defeat Eastern Tujue forces and blamed the lack of success on his deputy Han Sizhong (韓思忠), requesting that Han be executed.This event probably refers to Wei's commission in 701 as the commander of the forces in the Lingwu region, as the reference in Wang Jun's biographies in the Old Book of Tang and the New Book of Tang referred to Wei as the commander of forces in the Shuofang (朔方) region, which was centered around Lingwu. See Old Book of Tang, vol. 93 and New Book of Tang, vols. 61 and 111 . Wang, before Wu Zetian, argued that Wei, as the commander, should not divert all of the responsibility on his deputy. He also pointed out that Han was not in command and was brave and intelligent. Han was able to escape death, but as a result, Wang was sent out of the capital to serve as the magistrate of Weinan County (渭南, in modern Weinan, Shaanxi). When Wei was falsely accused by Wu Zetian's lovers Zhang Yizhi and Zhang Changzong of plotting treason in 703, however, Wang submitted a petition arguing that Wei was innocent, impressing his former colleague Song Jing for his fortitude.
