Historically, he is the 12th generation descendant of the Goryeo period general Kim Bang-gyeong (김방경, 金方慶; 1212–1300).In 1578, Gim passed the government military examination and was appointed as a training official.
In 1583, when Nitangjie (니탕개; 尼湯介), the Jurchen defect rebelled against the Joseon government in Hoeryeong, Gim rejoined the armed forces under General Jeong Eon-sin.
With this merit he was appointed Right Gyeongsang provincial army district Commander (경상우도병마절도사) and once again defeated the Japanese at Geumsan.
After three days of fighting, Gim was hit by a bullet on the side of his head and fell, unable to command his forces.
The Koreans were not in a good position since Gim Si-min was wounded and the garrison was now running low on ammunition.
However, Gwak Jae-u one of the main leaders of the irregular armies of Korea arrived at night with an extremely small band, not enough to relieve the Koreans at Jinju.
The Japanese general Ukita Hideie and Hosokawa Tadaoki commanding twenty-thousand troops, surrounded and besieged Jinju Castle.
For seven days and nights, the 3,800 Koreans defending the castle repeatedly repelled and defeated the Japanese, but Gim was killed in action from an arquebus round to the head.
Jinju Fortress, designated as a Historic Site of South Korea in 1963, includes a memorial to Kim Si-min.