Tatewaki was born in 1835, the third son of the head of the Kimotsuki clan, retainers to the Shimazu clan. He was adopted into the Komatsu clan at age 20, and at age 27, in 1862, he was named karô (House Elder) to the Shimazu clan. He then used that position to appoint Saigô Takamori and Ôkubo Toshimichi, among others, to important positions within the domain's government.
Following the Teradaya Incident, the Namamugi Incident, and the bombardment of Kagoshima by the British Royal Navy, Komatsu was determined to contribute to the rebellion against the shogunate, and to the restoration of an imperial government. On 1866/1/21, he served as mediator alongside Sakamoto Ryôma, as Saigô Takamori and Katsura Kogorô met to discuss and form the alliance between their domains. The following year, when Shogun Tokugawa Yoshinobu called the various daimyô to Nijô castle to discuss whether authority should be turned over to the Imperial Court, Tatewaki was among those in attendance, and among those who called for the shogunate to give up its power.
After the Meiji Restoration, Tatewaki held significant positions, including as a diplomat, but he died at the age of 37.
- Plaque at statue of Komatsu Tatewaki, in Kagoshima.