Matsudaira Katamori was born in the Yotsuya district of Edo, on February 15, 1836, at the residence of the Takasu Domain[2] He was the seventh son of Matsudaira Yoshitatsu [ja], daimyō of Takasu, born by one of Yoshitatsu's concubines, a woman of the Komori family whose name is believed by some scholars to be Komori Chiyo (she was also known by her Buddhist name, Zenkyō-in.

Though the Takasu domain was small, it had a high level of prestige due to its status as a branch family of the Tokugawa clan (through the gosanke house of Owari).

He was presented to the reigning shōgun, Tokugawa Ieyoshi, as well as to the Tairō Ii Naosuke, four months after his adoption, and at the end of the year was invested with the courtesy title of Wakasa-no-kami (若狭守), which was traditionally held by the heir to the house of Aizu.

[7] He also received the additional title of Sakonnoe-gon-shōshō (左近衛権少将; Lesser General of the Left Guard) from the Imperial court, and formally sent his thanks to the Emperor later that year.

Furthermore, Katamori inherited the family's traditional seat in the tamari-no-ma chamber, of Edo Castle where important matters of state were discussed in conjunction with the Senior Council.

The shogunate mobilized a massive number of men and ships from a broad coalition of feudal domains, and Aizu, being a prominent branch of the Shōgun's house and noted military power, was no exception.

[5] Samuel Wells Williams, a translator on the Perry mission, backs up this record: "Some of the flags seen ashore, and the red jackets, too, to-day had 會 on them.

Previously, the holder of the Kyoto shoshidai (京都所司代) position had held the highest power there, supervising affairs in the Kyoto-Osaka area as the representative of the Shōgun.

However, the successive Shoshidai, as well as the city magistrates under their charge, were increasingly unable to secure and maintain the public order, so the post of Shugoshoku was superimposed on the existing structure.

If we were to accept this assignment without question, and a one in ten thousand chance of disaster were to strike, we of the Aizu domain could not possibly do it all alone; the Shōgun would have to get involved, as would all of Japan.

Two of the domain-based councilors, Saigō Tanomo and Tanaka Tosa, were particularly opposed to the position, not only for the reasons that Katamori initially had opposed it, but also from a financial stance: Aizu, having been recently charged with both coastal defense at Edo Bay and supervision in eastern Ezo ( modern-day Hokkaidō), was heavily burdened by expense, and could not afford to do any more without risking total financial ruin.

[14] Saigo, ostensibly quoting the Chinese text Huai nan-tzu, described the intent to rein in the radicals as "trying to put out a fire while carrying brushwood".

The position was not without its personal incentives: it included an office salary of 50,000 koku a year, a 30,000 ryō loan to cover the expense of traveling to Kyoto, as well as a promotion to Senior 4th court rank, lower grade (正四位下; shō-shi'i-ge).

[18] Entering Kyoto on February 11, he first headed to Honzen-ji temple, changing into court clothes, then going to the residence of Imperial regent Konoe Tadahiro and paying his respects.

[18] Soon after his arrival, Katamori was again formally received by the Court, appearing before regent Konoe together with his senior retainers Ono Gonnojō and Komori Ikkan.

Katamori employed Prussian diplomat John Henry Schnell as an advisor and trader to procure and train his troops in western firearms.

[25] In total, twenty-two Japanese (samurai, peasants, farmers, and tradespeople) attempted to farm the 640-acre colony with lackluster results; the mulberry trees and tea bushes did not take to foreign soil.

[25] Katamori tried to achieve peaceful resolutions after the Battle of Toba–Fushimi, apologizing to the Imperial court many times, and even formally presenting a letter of submission to Prince Rinnoji no Miya Yoshihisa, but the members of the new Meiji government refused to pay him any heed.