The Shoku Nihongi first mentions Tanetsugu in 766, when he was promoted from to. Two years later, in 768, he was appointed as governor of Mimasaka Province. Thanks to the Shikike's staunch support of Emperor Kōnin's ascension, the family was successful in his court. Tanetsugu held various positions as a provincial governor, as well as civil and military roles, and was steadily promoted through the ranks, reaching in 781. After the deaths of his uncles Fujiwara no Yoshitsugu and Fujiwara no Momokawa, Tanetsugu came to represent the Shikike as the oldest grandson of Umakai. Along with the ascension of Emperor Kanmu in 781, Tanetsugu was promoted to. With the Emperor's deep trust, Tanetsugu was promoted quickly, joining the kugyō with a promotion to sangi in 782. In 783, he was promoted to, and in 784 was made chūnagon.
In 784, Kanmu wanted to move the capital away from Heijō-kyō. Tanetsugu recommended the location of Nagaoka-kyō as the spot for the new capital. By the Emperor's command, Tanetsugu inspected the site along with,,,, and Sakanoue no Karitamaro. Later that year, Tanetsugu was put in charge of the construction of the new capital. His appointment may have had the backing of his mother's family, the Hata clan, whose base of operations in Yamashiro Province was near the new capital site. Several members of the Hata clan were later promoted into the aristocracy based on their meritorious service in the construction.
Assassination
In 785, soon after the move of the capital, Tanetsugu was shot with an arrow while supervising the construction, and died the next day. Emperor Kanmu was absent at the time, visiting Yamato Province. Ōtomo no Takeyoshi was first arrested for the assassination, and after an investigation ten more people were executed, including Ōtomo no Tsuguhito and Saeki no Takanari. Ōtomo no Yakamochi, who had died a month before the incident, was identified as the ringleader and removed from the register of past officials. Several more people were implicated and exiled. Later, Prince Sawara was disinherited from his position as crown prince and exiled to Awaji Province, but died en route. There may have been discord between Sawara and Tanetsugu, but whether Sawara was actually involved in the assassination is not clear. A number of the officials involved in the assassination, including Takanari, were employed in the Crown Prince's Quarters. This incident, along with the fear of Sawara's vengeful ghost, contributed to the decision to move the capital again to Heian-kyō a short time later. Tanetsugu's final rank was, and he held the positions of chūnagon and director of the Shikibu-shō. He was 49 when he died. Emperor Kanmu posthumously promoted him to and sadaijin, and in 809 he was granted the additional posthumous position of Daijō-daijin.
Individuals punished in connection with the incident''[Nihon Kiryaku]''
