In 812, when the reign of the Emperor Saga became stable after the Kusuko Incident in the previous year, Sonohito was assigned to udaijin (minister of the right) which was the chief of Daijokan (Grand Council of State) in those days with the deep confidence of the emperor.
翌年の薬子の変を経て嵯峨天皇の治世が安定した812年（弘仁3年）、園人は天皇の厚い信任のもと、当時の太政官首班である右大臣に任官した。