Following his graduation from Saint-Cyr, MacMahon entered the French Army in 1827. He was assigned to the 4th Hussars Regiment in 1830. MacMahon subsequently participated in the French conquest of Algeria as a sous-lieutenant in the . He was commended for his capacity and bravery during the seizure of Algiers. On 24 November 1830, MacMahon further distinguished himself while serving with his regiment, during the , during the . He was awarded the Knight Order of the Legion d'honneur.