Stationed in French Indochina in 1945, he was beheaded by the Japanese during their March coup d'état.

In 1918, he transferred to the French Colonial Forces, subsequently serving with various regiments of the artillerie coloniale.

[1] Lemonnier declined to personally attend the event, although he allowed some of his staff to take part.

Lemonnier was subsequently taken prisoner himself and ordered by a Japanese general to sign a document formally surrendering the forces under his command.

[1] Lemonnier refused to sign the documents causing the Japanese to take him outside of Lang Son where they forced him to dig graves along with French Resident-superior (Résident-général) (Tonkin)[4] Camille Auphelle.