Monsabert graduated from Saint-Cyr military academy and was commissioned as a lieutenant in 1911.

Assigned to the 1st Mixed Rifle and Zouaves Regiment and then the 9th Zouaves March Regiment in the First World War, he finished the war at the head of a battalion and as a holder of the Legion of Honor.

Subsequently, he commanded the 3rd Algerian Infantry Division with the French Expeditionary Corps in the Italian campaign.

Monsabert led the II Corps with distinction for the remainder of the war in Europe.

From 1951 until 1955, Monsabert served as a deputy in the Rassemblement du Peuple Français political party in the National Assembly of France, representing the region Pyrénées-Atlantiques.