When Emperor Heizei was enthroned in 806, Kadonomaro's role as Togu no Daibu while the emperor was Crown Prince saw him promoted to the position of Gonsangi (a provisional deputy councilor) and then Sangi (councilor) while he also served as Shikibukyo (Minister of the Ministry of Ceremonies).
806年（延暦25年/大同(日本)元年）に平城天皇が即位すると、かつて皇太子時代の春宮大夫であった事から直ちに権参議に、続いて参議に昇任し、式部卿を兼ねた。