In 1931 Soglo voluntarily enlisted in the French Army. He fought during World War II, serving in Morocco and participating in the Allies' landings in Corsica, Elba, and southern France. Promoted to the rank of lieutenant, at the end of the war he was made a staff officer for the French Colonial Army. In 1947 he was attached to the French Ministry of Overseasas a military advisor. Securing the rank of captain on 1 January 1950, he was sent to French Indochina and fought in First Indochina War. He was awarded the Croix de Guerre in 1956 for his service during the war. While there he met a French-Vietnamese woman whom he later married. Following France's defeat in Indochina he was given the rank of major and station in Senegal, where he remained until 1960. After Benin achieved independence in 1960, Soglo was given the rank of colonel in the army and became the chief of staff under President Hubert Maga.