It is said that he had served for MINAMOTO no Yoritomo since Yoritomo raised an army, and was appointed as Shimotsuke no kami (Governor of Shimotsuke Province) in addition to Shugo (a provincial constable) of Harima Province, and the record in "Azuma Kagami" (The Mirror of the East) (a historical account of the Kamakura Shogunate) that the job position in the year of his death was Jugoinoge (Junior Fifth Rank, Lower Grade), Shimotsuke no kami might be a writing error because he was 'Saemon no jo' (third ranked office of the Left Division of Outer Palace Guards) or 'hangan' (judge) in his late years, whose court ranks were Jurokui (Junior Sixth Rank) or Jushichii (Junior Seventh Rank), and the court rank of his father, Masamitsu, was Shoshichii (Senior Seventh Rank).
源頼朝に挙兵の頃から仕え、播磨国守護に補されたほか、下野守にも任ぜられたとされるが、朝政の晩年の職位は「左衛門尉」や「判官」でありこれらは従六位か従七位の官位であること、また父・政光の官位も正七位下であったことなどから、卒年に従五位下下野守であったという『吾妻鏡』の記載は誤記の疑いがある。