Early in the Zhenyuan era (785-805) of Emperor Daizong's son Emperor Dezong, Quan served on the staff of Li Jian (李兼) the governor (觀察使, Guanchashi) of Jiangxi Circuit (江西, headquartered in modern Nanchang, Jiangxi).
As Emperor Dezong had also heard that Quan had a good reputation, he summoned Quan to serve as Taichang Boshi (太常博士), a consultant at the Ministry of Worship (太常寺, Taichang Si), and later as Zuo Bujue (左補闕), a low-level consultant at the Chancellory, also known as the Edict Examination Bureau (門下省, Menxia Sheng).
For example, in 792, following a major flood in the Guandong region (關東), the territory east of modern Sanmenxia, Henan, it was on Quan's advice that Emperor Dezong dispatched four imperial officials to comfort the victims.
[6] In 794, Quan became Imperial Archivist (起居舍人, Qiju Sheren), and was soon also put in charge of drafting edicts.
[4] He once pointed out that doing so was inappropriate — as the emperor needed to have multiple staff in charge of the task to avoid having a single person abuse power.
[4] Early in the Yuanhe era (805-821) of Emperor Dezong's grandson Emperor Xianzong, Quan Deyu served as the deputy minister of defense (兵部侍郎, Bingbu Shilang) and then deputy minister of civil service affairs (吏部侍郎, Libu Shilang).
[4] While serving as the minister of worship, there was an occasion when Yang Ping (楊憑) the mayor of Jingzhao Municipality (京兆, i.e., the Chang'an region) was indicted for corruption, exiled, and demoted to be a sheriff.
[4][8] In 811, when Emperor Xianzong asked the chancellors for their opinions on whether he should govern harshly or leniently, Quan advocated for a lenient rule, arguing that Qin dynasty was destroyed quickly due to its harshness and that Han dynasty persisted due to its leniency, further arguing that Tang itself survived various rebellions since the Anshi Rebellion because Emperor Taizong had been lenient and thus gained the deep loyalty of the people.
At this time, due to Emperor Xianzong's desire for effective governance, he granted great authority to the chancellors.
[4][9] In 816, Quan was made the military governor of Shannan West Circuit (山南西道, headquartered in modern Hanzhong, Shaanxi).
[4][7] In fall 818, he fell ill, and Emperor Xianzong issued an edict allowing him to return to his own mansion in Chang'an to recuperate.