During the Emperor Heizei era, FUJIWARA no Otsugu worked on political reforms, including establishment of the system of inspecting local governments, and rose to higher positions during the era of Emperor Junna (emperor after Saga) as uncle of Emperor (mother of Emperor Junna was FUJIWARA no Tabiko, sister of Otsugu), eventually was appointed to Udaijin (Minister of the Right) and Sadaijin (Minister of the Left) in a row.
平城朝においては観察使制度の設置等政治改革に積極的に取り組み、嵯峨朝を経て旅子を母とする淳和天皇が即位するとその外伯父として累進し、右大臣ついで左大臣に至った。