He was a Marine officer from 1968 to 1972 and served in Vietnam from October 1968 to October 1969, where he was awarded the Navy Cross, the Bronze Star, two Navy Commendation Medals for valor, two Purple Hearts, and ten air medals.
He graduated from Yale University in 1967 and was a Rhodes Scholar at Oxford University. After leaving Vietnam, Marlantes returned to Oxford where he continued his graduate education, earning a masters degree in philosophy, politics and education. He worked as a business consultant for various international energy companies.