Born in 1833 in Hagi, the eldest son of a Choshu domain physician, he was adopted at age eight by the samurai Katsura family and took the name Katsura Kogoro. He trained at the Meirinkan domain academy, rose to head of the Renbukan dojo in Edo under swordmaster Saito Yajiuro, and formed close ties with Yoshida Shoin. After the Ansei Purge (1858) he plunged into the loyalist movement. When Choshu forces were routed at the Kinmon Incident (1864), he spent nearly two years in hiding, evading the Shinsengumi and shogunate pursuers with the help of the Gion geisha Ikumatsu, who later became his wife. In 1866, mediated by Sakamoto Ryoma and Nakaoka Shintaro, he forged the Satsuma-Choshu Alliance — the diplomatic linchpin that broke the Tokugawa Shogunate's grip. After the Meiji Restoration he became a pillar of the new government. His two defining state-building acts: the 1869 Hanseki Hokan, by which all domain lords returned their lands and people to the Emperor, dismantling the feudal order; and the 1871 Haihan Chiken, the abolition of over 300 feudal domains and their replacement with a uniform prefectural system — a restructuring of Japan's governance comparable in scope to what took European nations centuries. He served as vice-chief envoy of the Iwakura Mission (1871-73), touring twelve Western nations and bringing back the institutional knowledge that shaped Meiji modernization. In his final years he grew increasingly troubled by political rifts and by the Satsuma Rebellion, and he died in Kyoto on May 26, 1877, aged 45. His deathbed bequest — donating his private farmland and forest in his home village of Itome for the education of local children — moved the villagers to found Kido Shrine (Yamaguchi City) in his memory. Counted alongside Saigo Takamori (emotion) and Okubo Toshimichi (will) as one of the Three Great Meiji Statesmen, he brought the indispensable quality of wisdom (chi) to the founding of modern Japan.

A cool-headed and systematic statesman who placed reason above emotion, acting with a long-term vision for the nation. He combined the steadiness of a trained swordsman with the flexibility of a skilled diplomat, always keeping the broad strategic picture in view. He consistently opposed impulsive hawkishness (the Korea debate) in favor of gradual internal reform. In his final years he suffered from what may have been nervous exhaustion, yet continued to record his candid thoughts in his diary to the end.

His three great state-building acts — the Satsuma-Choshu Alliance, the return of domain registers, and the abolition of feudal domains — dismantled three centuries of Edo-era feudalism and laid the skeletal structure of a unified modern Japan. He championed the shift toward constitutional government, planting the intellectual seeds that would flower in the Meiji Constitution. After his death Kido Shrine was built in Yamaguchi City to honor his memory and perpetuate his commitment to education. If Saigo moved the era with 'emotion' and Okubo with 'will,' Kido is remembered as the man who drew the blueprint of the modern state with 'wisdom.'