Born to a yangban family of the Gyeongju Kim clan, he was the son of another high-ranking official, Gim Man-gyun.
He passed the civil service examination with the highest score in 1561, and was made jwachamchan, a post of the second junior rank under the State Council.
He gained prominence in 1589 when he exposed the treachery of provincial official Jeong Yeo-rip, who was plotting to attack the capital.
Upon the outbreak of war in 1592, Gim took up military duty, leading the Joseon army to consecutive defeats at the capital and again at the Imjin River.
However, he remained vital to the royal family, as he led the army which guarded their retreat to Sunan in the far north following the surrender of Pyongyang.