Qi Kang was born in 740, during the reign of Emperor Xuanzong. His family was from Ding Prefecture. and claimed ancestry from the royal Jiang house of the Spring and Autumn period state Qi. His grandfather Qi Huan was a well-known commandery governor during Emperor Xuanzong's reign, although his father Qi Ao was described to have served in an insignificant position. In Qi Kang's youth, the Anshi Rebellion swept over the northern parts of the Tang empire, and he took his mother and fled to Kuaiji, where he spent his time studying. It was said that he was good at writing, particularly when it came to reports on various matters.
During Emperor Daizong's reign
During the Dali era of Emperor Xuanzong's grandson Emperor Daizong, Zhang Yithe prefect of Shou Prefecture invited Qi Kang to serve as an assistant. It was said that Qi was capable administratively and literarily, and Zhang respected him.
During Emperor Dezong's reign
Early in the Jianzhong era of Emperor Daizong's son Emperor Daizong, Zhang Yi became the governor of Jiangxi Circuit, and Qi Kang followed him and continued to serve on his staff. After Zhang later served a stint as chancellor and was made the military governor of Fengxiang Circuit in 782, he invited Qi to serve on his staff again. It was said that most of the military tactics that Zhang used at the time were suggested by Qi. In fall 783, when a mutiny at the capital Chang'an forced Emperor Dezong to flee to Fengtian, as Fengtian was a small city, Emperor Dezong considered further heading to Fengxiang. Meanwhile, Zhang, hearing of the mutiny and of Emperor Dezong's considering visiting Fengxiang, began undertaking preparations for the emperor's arrival. Qi Kang and fellow staff member Qi Ying pointed out that one of the military officers, Li Chulin, was previously a subordinate of the mutiny leader Zhu Ci and would be difficult to control. Zhang thus issued an order that Li report to Long Prefecture. Li, giving excuses, did not report immediately, and Zhang, concentrating on welcoming the emperor, never followed up on whether Li left for Long Prefecture. That night, Li and his associates mutinied and attacked Zhang's headquarters. Zhang and two of his sons climbed over the city walls and tried to flee, but were captured by the mutineers and killed. Qi Kang and Qi Ying both fled to Fengtian, and Emperor Dezong made Qi Kang an imperial censor with the title Shiyushi. After the rebellions were quashed in 784 and Emperor Dezong returned to Chang'an, the treasury was drained, and a major part of the empire was laid waste. At that time, the official Yuan Xiu, who was in charge of the state salt and iron monopolies, believed that Qi Kang was capable and recommended him as Cangbu Langzhong, a supervisorial official at the ministry of census, to be in charge of the salt monopoly in the Yangtze River-Huai River region. Qi was also soon made the deputy director of the supplies, in charge of supplying Chang'an with food from the Yangtze-Huai region. Soon, for minor faults that are lost to history, he was demoted to be the prefect of Chu Prefecture. He later served as the prefect of Su Prefecture before becoming the governor of Hunan Circuit was well as the prefect of its capital Tan Prefecture. He was later recalled to serve as imperial attendant and then the mayor of Henan Municipality. He later successively served as Mishu Jian, the director of the Palace Library and then the minister of worship. In 800, Qi was made Zhongshu Sheren, a mid-level official at the legislative bureau of government and given the designation Tong Zhongshu Menxia Pingzhangshi. This made him a chancellor, replacing the recently demoted Zheng Yuqing. While serving as chancellor, Qi suggested the abolition of the system where, after the ministry of civil service affairs selected officials to be commissioned, the officials from the legislative bureau and the examination bureau would reexamine the proposed list — reasoning that after the ministry of civil service affairs had carefully selected the officials, it would be a waste of time to reexamine. This suggestion was accepted. Per the customs of the time, as the deputy minister of rites was in charge of the imperial examinations, his relatives and friends would be given a separate imperial examination; under Qi's suggestion, that examination was also abolished. Also per Qi's suggestions, various local officials were also given titles of corresponding central government officials. Emperor Dezong also gave Qi the responsibilities of editing the imperial histories. It was said that while Qi was well-learned, he did not have long-term plans, but overly paid attention to details such that he became known for pickiness and harshness. In 803, after he became ill and offered to resign, he was made an advisor to Emperor Dezong's crown princeLi Song, and it was said that due to the illness, he was unable to thank Emperor Dezong in person. He died in 804 and was given posthumous honors. He was also given the posthumous name of Cheng.
