In the Battle of Sekigahara, Munenori belonged to the West squad and defended his residing castle, Kameyama-jo Castle, but when the West squad lost the final battle, he surrendered and handed over the castle in response to Kagetomo YAMAOKA's persuasion.
関ヶ原の戦いでは西軍に属し、居城の亀山城を守るが、本戦で西軍が破れ、山岡景友の説得に応じて降伏して城を明け渡した。