Born to a senior Satsuma retainer family, lords of the Yoshitoshi domain, he was adopted into the Komatsu family and rose to become a domain elder. Under Shimazu Nariakira and Hisamitsu he served at the core of domain administration, supporting Satsuma's modernization and enlightenment policies on the practical side. In the forging of the Satcho Alliance in 1866 he played a major behind-the-scenes role—accepting the mediation of Sakamoto Ryoma and Nakaoka Shintaro, and hosting the meeting between Saigo Takamori and Katsura Kogoro at his own Komatsu residence. With his strong language abilities he promoted the dispatch of Satsuma students to Britain (1865), contributing to the nurturing of later diplomats and businessmen such as Godai Tomoatsu and Terashima Munenori. After the Meiji Restoration he held posts including sanyo (official), judge of the Sotsairoku, and governor of the civil administration office, participating in administrative preparation before the abolition of domains, but he died of illness on August 16, 1870, at the young age of thirty-five. It is said that had Komatsu lived longer, he would have become a leading figure of the Meiji government alongside Saigo and Okubo. Reappraisal is growing of him as an outstanding practical administrator who supported Satsuma's modernization from behind the scenes.

Gentle, intelligent, and an outstanding practical administrator with a conciliatory style. He prized rationality over emotion and supported Satsuma's politics with a moderate approach different from Saigo's boldness or Okubo's forceful drive.

His behind-the-scenes contribution to forging the Satcho Alliance and his far-sighted promotion of Satsuma students studying in Britain had a major influence on Meiji Japan's modernization. His early death is lamented, and he is always mentioned in discussions of the 'what ifs' of modern Japanese history.