Soon after Prince Mochihito's conspiracy of uprising was exposed in May 1180, the order to put the prince in exile was given, and Mitsunaga and MINAMOTO no Kanetsuna lead the soldiers of Kebiishicho (Office of Police and Judicial Chief) to search and capture the prince at the Sanjo Takakura residence.
治承4年（1180年）5月、以仁王による挙兵の企てが露見し間もなく王に配流の命が下されると、源兼綱と共に検非違使庁の兵を率いて三条高倉邸に追捕に向かった。