Maurice Gamelin was born in Paris on 20 September 1872. Gamelin’s father, Zéphyrin, fought in the Battle of Solferino in 1859. From an early age Gamelin showed potential as a soldier, growing up in a generation seeking revenge on Germany for the annexation of Alsace-Lorraine at the end of the Franco-Prussian War.

Gamelin volunteered for service on 19 October 1891 before entering the military academy at Saint-Cyr on 31 October. In 1893, he graduated first in his class.

He began in the French tirailleurs with the 3rd Regiment based in Tunisia. He then joined the topographic brigade. When Gamelin came back to Paris in 1897, he entered the prestigious École Supérieure de Guerre and finished second of his class of about eighty of the best future officers in the French Army. Charles Lanrezac, then second-in-command of the École Supérieure de Guerre, and later a general in the early days of World War I, noted Gamelin as an intelligent, cultivated, and industrious young officer, bound to earn higher functions in the future. Gamelin joined the staff of the 15th Army Corps before commanding a company of the 15th battalion of the Chasseurs Alpins in 1904. He received the applause of his superiors for his diligence at manœuvre.

He published Philosophical Study on the Art of War in 1906, which critics praised, predicting he would become an important military thinker in the near future. He then became an attaché to General Joseph Joffre (a future Marshal of France) as he led the French forces during World War I). This position had been obtained with the help of Ferdinand Foch (also a future Marshal of France, as he led the Allied Forces to victory on the Western Front in 1918). These positions provided Gamelin with a solid knowledge of strategic and tactical warfare.

In 1911, Gamelin was given command of the 11th battalion of the Chasseurs Alpins in Annecy. However, in March 1914 he joined Joffre’s general staff (1914–18 called Grand Quartier Général). Early in the war, Gamelin helped draft the plans that led to the victory at the Battle of the Marne. He was promoted to lieutenant colonel and fought in Alsace on the Linge and later on the Somme. He became colonel in April 1916, and with good results on the battlefield was further promoted within eight months to the rank of brigadier general. He commanded the French 11th Infantry Division from April 1917 until the end of the war. In the region of Noyon, he showed sophisticated tactical skills by gaining ground without losing lives needlessly (which had been atypical earlier in the war, see Attaque à outrance).

Gamelin’s own views had changed from a purely defensive strategy relying on the Maginot Line. French strategists predicted a German drive across northern Belgium, as in 1914. Gamelin favoured an aggressive advance northward to meet the attacking German forces in Belgium and the Netherlands, as far removed from French territory as possible. This strategy, known as the Dyle Plan, fitted with Belgian defensive plans and also with British objectives. Gamelin committed much of the motorised forces of the French Army and the entire British Expeditionary Force (BEF) to this strategy. Such a strategy also meant that the most of the French Army would leave its one-year-old prepared defensive positions in northern France to be committed to joining battle on an unknown Belgian defensive line.

From 1919 to 1924, Gamelin was the head of the French military mission in Brazil. He then commanded the French Army in the Levant, now Syria and Lebanon. He was the commander of the 30th Military Region in Nancy from 1919 to 1931, when he was named head of the general staff of the French Army. In 1932 he knew the Reichswehr mobilization plan was to at least treble their force, but lacked intelligence on the armament plan, the militia plan, or the Manstein Plan. He prepared France’s military until the beginning of World War II, although challenged by restricted funding (→ Great Depression in France) and by the political inertia regarding German re-armament and later the Third Reich, which was intensified after the end of the Allied occupation of the Rhineland and its remilitarisation. At the outbreak of the war in September 1939, Gamelin was considered one of the best commanding generals in Europe, and was respected even among the Wehrmacht.

When war was declared in 1939, Gamelin was France’s commander in chief, with his headquarters at the Château de Vincennes, a facility completely devoid of telephonic, or any other electronic, links to his commanders in the field.; a massive oversight in the face of the Wehrmacht’s subsequent swift and flexible ‘Blitzkrieg’ tactics. France saw little action during the Phoney War, apart from a few French divisions crossing the German border in the Saar Offensive, who advanced a mere 8 km (5.0 mi). They stopped even before reaching Germany’s unfinished Siegfried Line. According to General Siegfried Westphal, a German staff officer on the Western Front, if France had attacked in September 1939 German forces could not have held out for more than one or two weeks. Gamelin ordered his troops back behind the Maginot Line, but only after telling France’s ally, Poland, that France had broken the Siegfried Line and that help was on its way. Before the war, he had expected the Polish Army to hold out against Germany for six months. Gamelin’s long-term strategy was to wait until France had fully rearmed and for the British and French armies to build up their forces, even though this would mean waiting until 1941. He prohibited any bombing of the industrial areas of the Ruhr, in case the Germans retaliated. The French mobilisation had called up many essential workers, which disrupted vital French industries in the first weeks of the campaign.

The Dutch surrendered within five days of being attacked, the Belgians in 18 days (“campagne des 18 jours”), and the French were left with only a rump of their former army to defend their nation. Gamelin was removed from his post on 18 May 1940 by Paul Reynaud, who had replaced Édouard Daladier as Prime Minister in March. The 68-year-old Gamelin was replaced by the 73-year-old Maxime Weygand, who crucially delayed planned counter-attacks before eventually launching them.

Gamelin died in Paris in April 1958 at the age of 85.