He took initiative in Ansei no Taigoku (the suppression of extremists by the Shogunate) and was assassinated outside the Sakuradamon Gate by a feudal retainer of the Mito Domain (the Sakuradamongai Incident), who then left the domain in opposition of Ansei no Taigoku.
安政の大獄を行なって反対派を処罰したが大獄に対する反発から桜田門外において水戸藩脱藩藩士らに暗殺された（桜田門外の変）。