On April 23, 1858, Naosuke was appointed to Tairo (chief minister) of the Edo bakufu through the political maneuvering of certain members of the Nanki Group (a group supporting Yoshitomi from the Kishu-Tokugawa family), such as Tadakata MATSUDAIRA and Tadanaka MIZUNO.
松平忠固や水野忠央（紀州藩付家老）ら南紀派の政治工作により　安政5年（1858年）4月23日、直弼は江戸幕府の大老に就任した。