Kim Jong-gak was born in Jungsan County, South Phyongan Province on 20 July 1941, and joined the Korean People's Army in August 1959.

In 1992 his duties grew again: in April, during Kim Il Sung's 80th birthday, he was promoted to colonel-general, and in December he was appointed vice-minister of the People's Armed Forces.

He was appointed administrator of the KPA's parades and performances in Pyongyang, elected deputy to the Supreme People's Assembly starting from 1998, and promoted to general in April 2002.

In 2007, he was appointed first vice-director of the KPA General Political Bureau; starting from that year, he frequently accompanied Kim Jong Il in his inspection tours.

On 9 February 2018, North Korean media confirmed that Kim had replaced Hwang Pyong-so as the Director of the General Political Bureau of the KPA and was given back his party Politburo seat.