Kenshin took over the family headship of the Uesugi clan from Norimasa UESUGI, who was a Kanto Kanrei (a shogunal deputy for the Kanto region), he thereafter changed his name to Masatora UESUGI, and was later appointed to Kanto Kanrei, an important post in the Muromachi bakufu (Japanese feudal government headed by a shogun) which is inherited by the Uesugi clan.
のちに関東管領上杉憲政から上杉氏の家督を譲られ、上杉政虎と名を変えて上杉氏が世襲する室町幕府の重職関東管領に任命される。