In the period of the Third Shogun MINAMOTO no Sanetomo, Kagemori took an active part as a close adviser who was much trusted by Sanetomo and Masako, and battled as a member of the Hojo clan at the Shigetada HATAKEYAMA Rebellion in 1205 and at the Battle of WADA in 1213.
3代将軍・源実朝の時代には実朝・政子の信頼厚い側近として活躍し、元久2年（1205年）の畠山重忠の乱、建暦3年（1213年）の和田合戦では北条方として戦う。