In 762, Fujiwara no Nakamaro was at the peak of his success, and while his three sons were promoted to sangi, the 47-year-old Sukunamaro was resigned to his rank of ju go-i no ge.
Sukunamaro conspired with Ōtomo no Yakamochi, Saeki no Imaemishi, and Isonokami no Yakatsugu in a plot to assassinate Nakamaro, but the plan was discovered.
In 764, Fujiwara no Nakamaro incited a rebellion, and Sukunamaro, in response to an Imperial decree, gathered several hundred soldiers and assisted in putting it down.
In 771 the sadaijin Nagate died, and Yoshitsugu's support of Kōnin left him as the central figure of the Fujiwara clan.
When his grandson Emperor Heizei assumed the throne, Yoshitsugu was posthumously promoted to shō ichi-i (正一位), the highest rank under ritsuryō, and daijō-daijin.