In 807, successfully becoming a monjosho (student of Literary Studies in the Imperial University), Sadanushi was appointed as Dainaiki (Senior Secretary of the Ministry of Central Affairs) in 815 whereby, with his father, he received the title of Ason (the second highest of the eight hereditary titles) and was given the surname in 823.
大同(日本)2年（807年）に文章生に及第し、弘仁6年（815年）に大内記となり弘仁14年（823年）には父とともに朝臣に改め、姓を賜った。