Afterward, backed by his father's power, he successively held various important posts and when he concurrently held the posts of Sashoben (Minor Controller of the Left), Kurodo (Chamberlain), Saemon no Gon no Suke (Provivsional Assistant Captain of the Left Division of the Outer Palace Guards) and Togu Gakushi, TAIRA no Nobunori wrote in the December 3, 1157 entry of his diary "Heihanki," that Toshinori was 'one of a kind.'
以後、父の権勢をも背景として要職を歴任し、左少弁蔵人、左衛門権佐、東宮学士を兼帯した際には「希代」のことと評された（『兵範記』・保元2年（1157年）10月23日条）。