He hailed from a very poor family in Donghai 東海 (modern Tancheng 郯城, Shandong) but was fond of learning. During the local examinations in the search for potential candidates for state offices he demonstrated his intelligence when he pointed at some discrepancies in the texts presented. He was therefore made clerk (zhanggu 掌故) of the Chamberlain for Ceremonials (taichang 太常) and was soon made head of the academy in Pingyuan 平原 (modern Pingyuan, Shandong). Grand Mentor of the Heir Apparent (taizi taifu 太子太傅) Xiao Wangzhi 蕭望之 recommended him to the emperor, but Emperor Xuan 漢宣帝 (r. 74-49 BCE) did not like Confucian scholars very much.
Only when Emperor Yuan 漢元帝 (r. 49-33 BCE) succeeded to the throne, Kuang Heng was made gentleman of the interior (langzhong 郎中), later erudite (boshi 博士) of the National University (taixue 太學) and then palace steward (jishizhong 給事中).
With his educational background, he often submitted memorials quoting from the Confucian Classics how an excellent government would look like, and criticized prodigy and corruption prevailing in these days. Emperor Yuan thereupon made him Grand Master of Splendid Happiness (guanglu dafu 光祿大夫), then Junior Mentor of the Heir Apparent (taizi shaofu 太子少傅), and finally Censor-in-chief (yushi dafu 御史大夫).
During the reign of Emperor Cheng 漢成帝 (r. 33-7 BCE), Kuang Heng decided to fight against the director of the Imperial Secretariat (shangshu ling 尚書令), Shi Xian 石顯, who had usurped the control of all political decisions. Shi Xian fought back, and highly intimidated, Kuang Heng expressed his wish to retire, yet the Emperor refused. In 30 BCE he was accused of corruption and demoted to a commoner.