His family was from Hezhong Municipality (河中, in modern Yuncheng, Shanxi)[2] and claimed ancestry from the Han Dynasty scholar Dong Zhongshu.
Later, he was made the secretary general at the ministry of armory supplies (衛尉丞, Weiwei Cheng), and then the military advisor to the prefect of Fen Prefecture (汾州, in modern Linfen, Shanxi).
Subsequently, when the prefect, Cui Yuan, was made the military governor (Jiedushi) of Huainan Circuit (淮南, headquartered in modern Yangzhou, Jiangsu), he invited Dong to serve as his secretary.
[5] Soon, though, he was recalled to Chang'an to serve as an imperial censor, first under the title Dianzhong Shiyushi (殿中侍御史) and then Shiyushi (侍御史); he later successively served as Zhuke Yuanwailang (主客員外郎), a low-level official at the ministry of rites (禮部, Lǐbu); and then Cibu Langzhong (祠部郎中), a supervisorial low-level official at the ministry of rites.
Because he had a reputation for being hardworking and careful, he was subsequently made You Sanqi Changshi (右散騎常侍), a high-level consultant at the legislative bureau (中書省, Zhongshu Sheng) as well as deputy chief imperial censor (御史中丞, Yushi Zhongcheng), but acting as the chief imperial censor.
Soon, he was made the prefect of Hua Prefecture (華州, in modern Weinan, Shaanxi) as well as defender of Tong Pass.
[4] After Chang'an was recaptured from Zhu, Dong accompanied Emperor Dezong back to Chang'an and was made a general of the imperial guards, and then Shangshu Zuo Cheng (尚書左丞), one of the secretaries general of the executive bureau (尚書省, Shangshu Sheng).
At that time, his colleague as secretary general, Yuan Xiu (元琇), was in charge of financial affairs, but was demoted due to false accusations by the chancellor Han Huang.
He also gave both Dou and Dong the designation Tong Zhongshu Menxia Pingzhangshi (同中書門下平章事), making them chancellors de facto.
[2][10] In 796, Li Wanrong (李萬榮) the military governor of Xuanwu Circuit (宣武, headquartered in modern Kaifeng, Henan) died.
At that time, the military governors of Xuanwu were accustomed to have a large corps of guards, and Dong dismissed them as he believed them to be unnecessary.
[11] Meanwhile, Emperor Dezong, believing Dong to be too meek in his personality, sent Lu Changyuan (陸長源) to assist him as the commander of the army.