He hailed from Yunyang 雲陽 (modern Chunhua 淳化, Shaanxi) and was a secretary (sheren 舍人) of Prince Liu Xin 劉欣. When Liu Xin Xin mounted the throne (posthumously known as Emperor Ai), Dong Xian was made a court gentleman (lang 郎). Emperor Ai loved his elegant appearance and appointed him palace attendant commandant-escort (fuma duwei shizhong 駙馬都尉侍中).
In 3 BCE, Dong found out that the Prince of Dongping 東平, Liu Yun 劉雲, planned a rebellion, and notified this to the emperor, together with Sun Chong 孫寵 and Xi Fugong 息夫躬. Dong Xian was rewarded with the title of Marquis of Gao'an 高安侯.
In 2 BCE, Dong was appointed Commandant chamberlain for the palace garrison (weiwei jiangjun 衛尉將軍), a year later Minister of War (dasima 大司馬). Dong Xian was a constant companion of the Emperor, and even his wife was allowed to enter the inner chambers of the palace. His daughter was made an imperial concubine of the zhaoyi 昭儀 rank (see female officials), his male relatives were all given high posts in the capital. Additionally, Dong Xian was able to amass a large fortune and to support hundreds of retainers.
Imperial favour went so far that Dong Xian was even allowed to prepare his tomb adjacent to Emperor Ai's own tomb mound Yiling 義陵. The utmost sign that Emperor Ai had totally lost his head was his plan to cede the throne to Dong Xian. When Emperor Ai died prematurely, Grand Empress Dowager Wang 王太后 dismissed Dong Xian from all offices, and Dong Xian, sensing that the end of his career had come, committed suicide with his wife. His male relatives were banished to Hepu 合浦 in southern China.