Kyoto
Katamori was born as a son of Lord Matsudaira Yoshitatsu of Takasu han. He was adopted by Matsudaira Katataka of Aizu han in 1846.
In 1862, he was apointed as the Military Commissioner of Kyoto and took 1000 Aizu Samurai to Kyoto in December.
1863 August, he succeeded to expel Choshu han lobbyists from the imperial court and he got great trust from Emperor Komei.(Political change on August 18.)
While in Kyoto, he used the Shinsengumi to maintain public peace.
1867, Shogun Tokugawa Yoshinobu returned political power to Emperor Meiji and the Military Commissioner of Kyoto was abolished.
The Battle of Aizu
Katamori left Kyoto during the Battle of Toba-Fushimi with Shogun Yoshinobu and returned to Aizu in february. Pro-Emperor troops defeated the Bakufu troops in Ueno (the Battle of Ueno) and headed to north in May. The han in northern provinces allied together to against the Pro-Emperor troops which were mainly Satsuma han and Choshu han. However some of the han went over to the Pro-Emperor side and most han surrendered before Aizu fell.
Meiji
After the Boshin War, Katamori confined himself until 1872 and became the chief priest of Nikko Tosho Gu in 1880. Katamori died of Pneumonia in 1893, he kept a letter from Emperor Komei with him all the time but he never talked about Bakumatsu.