In the Hogen Rebellion, in 1156, while his father Tameyoshi, his brothers Yorikata and MINAMOTO no Tametomo were allied with the Emperor Sutoku, Yoshitomo allied with the Emperor Goshirakawa with TAIRA no Kiyomori, and won the war.
保元元年（1156年）の保元の乱の際に崇徳天皇方の父為義、弟の頼賢・源為朝らと袂を分かち、平清盛と共に後白河天皇方として戦い勝利する。