In 1840, he was given the courtesy title of Wakasa-no-kami and Lower 4th, Junior grade court rank.
This was one of the causes of Ii Naosuke's Ansei Purge, and Tadaaki was forced to resign as Kyoto Shoshidai in 1850.
During this period, he served as chief intermediary between the shogunate in Edo and Emperor Kōmei during a period of extensive negotiations, delays, and political maneuvering which accompanied plans for the eventual marriage of Komei's sister, Princess Kazunomiya, and Tokugawa Iemochi in March 1862.
[5] He resigned again in 1862, this time also from the position of daimyō, adopting Sakai Tadauji, the son of a hatamoto as his heir, and went into retirement.
However, with the start of the Boshin War, following the defeat of the Tokugawa shogunate forces at the Battle of Toba-Fushimi, he resumed the post of daimyō and defected to the Imperial side.