His grandfather Cui Junsu (崔君肅) as a mid-level official under the Tang dynasty's founder Emperor Gaozu.
[1] As of Wu Zetian's Tianshou era (690-692), Cui Yuanzong was serving as the minister of justice (秋官尚書, Qiuguan Shangshu).
However, he was also said to be, while appearing to be lenient on the outside, actually very harsh as a judge, and he picked faults with people and gave them heavy punishments, and therefore was feared.
At a later point, after a general pardon, he was recalled and served as imperial censor (監察御史, Jiancha Yushi).
During Emperor Zhongzong's reign, Cui successively served as Shangshu Zuo Cheng (尚書左丞) -- a secretary general of the executive bureau (尚書省, Shangshu Sheng), and as the prefect of Pu Prefecture (蒲州, roughly modern Yuncheng, Shanxi), before retiring on account of age and illness.