He was from the "Lesser Branch" of the prominent Cui clan of Qinghe (清河, in modern Xingtai, Hebei), and his ancestors originally claimed ancestry from the ruling house of the Spring and Autumn period state Qi.
[3][4] After that, Cui was recalled to the capital Chang'an to serve as the deputy minister of public works (工部侍郎, Gongbu Shilang), and an imperial scholar at Jixian Hall (集賢殿)[3] — an event that the Old Book of Tang also described and placed in 834, while further mentioning at that time, he was also made acting minister of rites (禮部尚書, Libu Shangshi).
According to the Old Book of Tang, he thereafter served as deputy minister of defense (兵部侍郎, Bingbu Shilang), and also was put in charge of selecting officials for the eastern capital Luoyang.
In 837, Cui was sent out of Chang'an to serve as the governor (觀察使, Guanchashi) of Xuanshe Circuit (宣歙, headquartered in modern Xuancheng, Anhui), as well as the prefect of its capital Xuan Prefecture (宣州).
[2] In fall 839, Cui Dan, while still serving as the minister of worship, was made a chancellor de facto with the designation Tong Zhongshu Menxia Pingzhangshi (同中書門下平章事).
[5] He thereafter was also made Zhongshu Shilang (中書侍郎), the deputy head of the legislative bureau, and given the honorary title Yinqing Guanglu Daifu (銀青光祿大夫).