As Military Governor of Paris he played an important role in the First Battle of the Marne, when Maunoury's Sixth Army, which was under his command, attacked the German west flank.

From October 1915 he served as Minister of War, resigning from that post in March 1916 after criticizing the performance of the French Commander-in-Chief, Joseph Joffre (formerly his subordinate, earlier in their careers), during the German attack on Verdun.

[16] In 1886, he had risen to the rank of lieutenant-colonel,[17] and was later appointed governor of the French Sudan, during which time he successfully quelled a rebellion by Sudanese insurgents under Mahmadu Lamine.

Also in 1906 he became a member of the Conseil Superieur de la Guerre (the Superior War Council, a body of senior generals chaired by the President).

[29] Following Michel's removal Gallieni, who was the preferred choice of Prime Minister Caillaux, declined the job of Army Chief of Staff.

[37] In the same year, Gallieni was considered the logical choice for supreme commander of the French Army, but because of advanced age and poor health, he declined in favour of Joffre.

Messimy imagined that Joffre would be more likely to listen to his former superior, but he was quickly palmed off onto the staff officer General Belin and his deputy Berthelot.

However, on that day Viviani formed a new government (Union sacrée), and on 27 August the new War Minister Millerand (who had replaced Messimy largely because of the poor state of the Paris defences) visited Joffre, who promised to provide the three corps if Maunoury's attack should fail.

Joffre also added Drude's 45th Division of Zouaves from Algeria, who made a huge impression marching through Paris, and IV Corps from Third Army.

Paris, 3 September 1914 Gallieni believed that Joffre's strategy of retreating behind the Seine was "divorced from reality" as the Germans would not allow his forces enough time to rally.

That morning Gallieni set engineers and civilian labourers to work cutting down woods and trees, and preparing bridges and buildings for demolition to clear lines of sight for guns.

[61][62][63] On the night of 3–4 September Joffre sent a handwritten note to Gallieni, wanting Maunoury's Sixth Army to push east along the north bank of the Marne, although not specifying a date.

This was in line with his modification of Instruction General No 4 (2 September), envisaging a giant pocket from Paris to Verdun, of which he enclosed copies to Gallieni.

They arrived at 3 pm and with some difficulty located Murray, who had no idea when Sir John, who was out visiting British I Corps, was to return and was unwilling to make any decision in his absence.

In a three-hour meeting, the French generals proposed that Sixth Army was to move that afternoon, then on 5 September was to strike German IV Reserve Corps on the west flank.

A provisional agreement was drawn up, with copies kept by Maunoury, Gallieni, and Lt-Col Brecard to take to GQG for Joffre's approval.

The French came away with the impression that the British would not cooperate and that Murray had "une grande repugnance" for them, but he did in fact pass the plans along to Sir John.

Upon seeing the "taxicab army" ferrying troops to the front, Gallieni made one of the most oft-quoted remarks of the First World War: "Eh bien, voilà au moins qui n'est pas banal!"

The Germans, concerned at the gap between their First and Second Armies, began to pull back on 9 September, giving the Allies a strategic victory in the Battle of the Marne.

[87] Early in 1915 Gallieni supported the proposal of Franchet d’Esperey and Aristide Briand (Justice Minister) for an expedition to Salonika, which he hoped would detach first Turkey then Austria-Hungary, leaving Germany "doomed."

They rejected the proposal prepared by his staff to vest authority in the Minister of War, Briand objecting that he would be obliged to answer questions in the Chamber about operational matters.

[100] Gallieni made an effort to unite soldiers and politicians, and to establish a working relationship in which he concentrated on supplying resources (not dissimilar to the role to which Kitchener was restricted in the UK from the end of 1915).

[101] However, Gallieni had prostate cancer, with pain making him less tolerant of criticism at a time when political disquiet was growing after the failure of the Second Battle of Champagne, especially the failed attack on Hartmannswillerkopf and its subsequent total loss.

[105] In autumn 1915 Lt-Colonel Driant, a member of the Chamber of Deputies and commander of a chasseurs brigade, complained to Gallieni of how Joffre had been removing guns and garrisons from Verdun and even preparing some forts for demolition.

Gallieni demanded to see all paperwork from the period, but Joffre had made no such order in writing, merely despatching de Castelnau to assess the situation.

Gallieni launched an angry report at the Council of Ministers on 7 March—read in his usual precise way—criticising Joffre's conduct of operations over the last eighteen months and demanding ministerial control, then resigned.

[114] There is also a Camp Galieni in Abidjan that serves as the Ivorian Arms forces Headquarters [115] Clayton describes him as a dry precise man, a secular republican (views which influenced his colonial policy) but one who kept aloof from politics.

[116] Herwig describes him as "formidable" and "France’s most distinguished soldier" whose "physical appearance alone commanded respect": he was of straight bearing and always wore full dress uniform.

[117] By the time Gallieni complained about Joffre's handling of Verdun, there was already public debate, much of it politically motivated, about which of them had "won" the First Battle of the Marne in 1914.

Ian Senior describes "Gallieni's claims" as "absolute nonsense" and Lyet's book as "an excellent analysis which convincingly refutes" them.