In 1852, Katsura went to Edo (present-day Tokyo) to study swordsmanship, established ties with radical samurai from the Mito Domain (present-day Mito, Ibaraki Prefecture), learned artillery techniques with Egawa Tarōzaemon, and (after observing the construction of foreign ships in Nagasaki and Shimoda), returned to Chōshū to supervise the construction of the domain's first western-style warship.

He spent the next five days in hiding under Nijō Bridge along the Kamo River, posing as a beggar, his lover would bring him rice balls from the shop of the Chōshū merchant Imai Tarōemon and later aided in his escape.

After radical elements under Takasugi Shinsaku gained control of Chōshū politics, Katsura, under the new name Kido Junichirō (木戸 準一郎) was instrumental in establishing the Satchō Alliance with Saigō Takamori and Ōkubo Toshimichi through the mediation of Sakamoto Ryōma in 1866, which proved to be critical in the Boshin War and the subsequent Meiji Restoration.

On 23 December 1871, he accompanied the Iwakura Mission on its round-the-world voyage to America and Europe,[2] and was especially interested in Western educational systems and politics.

Kido lost his dominant position in the Meiji oligarchy to Ōkubo Toshimichi, and resigned from government in protest of the Taiwan Expedition of 1874, which he had strenuously opposed.

During the middle of the Satsuma Rebellion in 1877, he died of Colorectal cancer that had been plaguing him for a long time, which consisted of a combination of some form of mental disease and physical exhaustion, years of excessive alcohol consumption as well as an illness assumed to be tuberculosis or beriberi.

With his dim consciousness, Kido shook Okubo's hand and said, "Enough Saigo " He is enshrined at Kyoto Ryozen Gokoku Shrine, where his tomb is located.

Kido's diary reveals an intense internal conflict between his loyalty to his home domain, Chōshū, and the greater interest of the country.

He wrote often of having to fight rumors at home that he had betrayed his old friends; the idea of a nation was still relatively new in Japan and so the majority of samurai cared more for securing privileges for their own domain.

While still portrayed as a ruthless radical leader of the Chōshū clan, he serves as a benevolent mentor of sorts to the young Himura Kenshin, who worked under him as the Hitokiri Battōsai.

He also appears in the video game Ryū ga Gotoku Ishin!, portrayed by the Yakuza character Shun Akiyama, and voiced by Kōichi Yamadera.

Katsura Kogorō has also a prominent supporting role in Team Ninjas 2024 Action-RPG Rise of the Rōnin and is one of the many popular personalities from the Bakumatsu-Period, that the player can get acquainted with.