Kim Nam-Gu made his international sport shooting début for South Korea in 1966, when he took part in trap shooting at that year’s World Championships. He later took part in the trap competition at the 1972 Munich Olympics, placing 41st in a field of 57 competitors. He had more success two years later, however, when he won a bronze medal in team trap at the 1974 Asian Games, alongside the non-Olympians Choi Jung-yong, Lee Chong-tae, and Yun Moo-ung. Although he retired from international competition shortly thereafter, he continued to compete domestically into his 80s. In 2007, at the age of 84, he was the oldest active shooter in the South Korean national federation. By career, he was a successful businessman.
Republic of Korea