Louis McMillan graduated from the US Naval Academy in 1952, where he was on the crew team. He was on active duty for 14 years, was a veteran of the Korean War, and remained with the US Naval Reserve until 1982, retiring as a captain. He graduated from the Naval Postgraduate School in Monterey, California in 1962, and after his active duty service he worked as a research analyst for the defense company Vertex Corp, and later for the Center for Naval Analyses. He retired in 1994 after working for a few years for Syscon Corp., a defense contractor, and later settled in Destin, Florida.