Even before his birth, he was designated to be adopted by Matsudaira Katsuyoshi, the daimyō of Iyo-Matsuyama Domain and this was officially announced on November 25, 1837.

In 1839, Yoshinaga began implementation of a fiscal austerity plan in an effort to resolve the perennial financial difficulties of Fukui Domain.

In January 1840, with the discharge of Matsudaira Shume, reformists such as Nakane Yukie, Yuri Kimimasa and Hashimoto Sanai took a leading role in domain politics.

Yoshinaga performed innovative work such as establishment of a translation bureau "Yoshō-shūgaku-sho" to acquire rangaku knowledge and spur military modernisation.

When the succession problem of 14th Shōgun arose, he delegated his retainer Hashimoto Sanai to Kyoto in support of Tokugawa Yoshinobu, the lord of the Hitotsubashi-Tokugawa family.

However, with the appointment of Ii Naosuke to the position of Tairō, Yoshinobu's faction was defeated and Tokugawa Iemochi (of the Kishu-Tokugawa family) became Shōgun.

The Ii clan of Hikone Domain and the Echizen-Matsudaira clan of Fukui Domain had had a strong enmity for several generations, and relations between the Tairō worsened further after Ii pushed through the ratification of Treaty of Amity and Commerce between US and Japan without acceptance by Emperor Kōmei.

The assassination of Ii Naosuke in the Sakuradamon Incident changed the Shogunate's policy, allowing Matsudaira Shungaku to return to politics in April 1862.

In 1862, Shungaku formed the Rōshigumi, a group of rōnin organised as a paramilitary militia to help guard Shogun Tokugawa Iemochi on his 1863 trip to Kyoto.

He also invited Yokoi Shōnan from Kumamoto Domain as a political consultant, and planned for Shogun Tokugawa Ieshige to relocate to Kyoto.

This congress intended to diminish the power of the Shogunate and establish a council system of government by the Imperial Court together with select major domains.