He graduated from St. Cyr in 1877 and entered active duty as an infantry officer in North Africa.
Sarrail's conventional military career took a highly unconventional turn in the 1890s. As a battalion commander, he became a Radical, a Freemason, and a supporter of Dreyfus, known, both within the army and in political circles, as an outstanding exception to the clerical and sentimentally monarchist officers who dominated the army's leadership.
Between 1900 and 1907 Sarrail served in the War Ministry under the reforming General André, commanded the infantry school at St. Maixent where sergeants were trained to rise to officer's rank, and took charge of the military guard at the Chamber of Deputies. He was the director of infantry at the War Ministry from 1907 to 1911, and in 1914 as a major general entered the war as commander of the VI Corps at Chalons. His advancement depended in part on his recognized organizational skills, but his political sympathies and open ties to the important Radical party in the Chamber of Deputies unquestionably aided his career.
Sarrail's VI Corps, as part of General Ruffey's Third Army, advanced northward in a counterattack against the Germans in the lower Ardennes. After a bitter encounter battle (August 22) at Vitron, Sarrail was forced backward to Verdun. Ruffey's lack of composure led General Joffre to replace him with Sarrail. The new commander of the Third Army distinguished himself with a tenacious defense of Verdun, rejecting Joffre's suggestion that the Third Army retreat from the crucial fortress if German pressure grew too great. Verdun became the eastern anchor for the French forces during the battle of the Marne.
Sarrail's role enhanced his popularity among leaders of the political Left who began to present him as a desirable successor to Joffre.
In June and July 1915, Sarrail's Third Army suffered a sudden defeat when the Germans reopened operations in the quiescent Argonne sector. Joffre took the occasion to relieve his politically troublesome subordinate, but Sarrail's political contacts and his symbolic role as the leading republican general in the army made this the occasion for a governmental crisis. Sarrail and his supporters were placated when he was offered command of the French forces at Gallipoli, but in light of the rapidly deteriorating situation in the Balkans in September 1915, Sarrail instead became commander of the French forces in Macedonia. He reached Greece in time to launch an offensive up the Vardar valley in October 1915. It was too late, however, to serve its intended purpose of aiding the Serbs, who were being crushed by invading German and Bulgarian armies.
For the next two years, Sarrail and his Army of the Orient remained a center of political and military controversy, which soon involved France's allies as well. Sarrail stood as the favorite general of the political Left, shielded from repeated attempts by Joffre to control him. The Army of the Orient, for which Sarrail demanded reinforcements, became a bone of contention between Allied political and military leaders like Joffre, who favored concentrating all energies on the western front, and those like Prime Ministers Briand and Lloyd George, who hoped other fronts could provide the key to victory. Moreover, Sarrail took an active role in manipulating the Greek political scene to secure his base of operations at Salonika.
In December 1915, Joffre became commander in chief of all French armies, including the Army of the Orient. His deputy, General de Castelnau, was sent to Greece in an unsuccessful effort to assert Joffre's authority over Sarrail. In early 1916 in the face of numerically superior Bulgarian forces Sarrail and his British allies moved to secure their position at Salonika by constructing a fortified perimeter seventy miles long. At the same time, Sarrail gradually took over de facto civil administration of the port of Salonika and its environs despite protests from the Greek government. In France, criticism of Joffre led to a reassessment of French military leadership in a closed session of the Parliament in July 1916; representatives of the political Left combined their attacks on Joffre with praise for Sarrail.
Sharp fighting broke out on the Salonika front in the fall of 1916 as the Bulgarians launched a major attack. Sarrail, reinforced by Serbian and Russian contingents and empowered by the British government to direct British forces in Macedonia, counterattacked with spectacular success. Despite heavy losses, Sarrail's forces pushed through difficult mountain terrain to capture Monastir in southern Serbia on November 19. The first important Allied victory in months, the Monastir offensive failed to help beleaguered Rumania, but it reinforced Sarrail's virtually autonomous position in the French army. During these fall months of 1916 Sarrail encouraged an indigenous revolt against the pro-German King Constantine, which culminated with the establishment of a pro-Allied government led by Prime Minister Venizelos.
In 1917 Sarrail's military career reached its peak, followed by utter collapse. In January the Rome conference of political and military leaders from France and Britain formally designated Sarrail as commander in chief of the Allied Army of the Orient. In a preview of the arrangement established on the western front in 1918, all national commanders in Macedonia and Salonika were placed under his direction, while retaining the right to appeal decisions to their respective governments. Sarrail's spring offensive thus utilized Serbian, Russian, Italian, and British forces as well as French contingents. It failed completely. The poorly coordinated attack was carried out by exhausted and dispirited troops over impossible terrain, and the Bulgarians easily held their position on the Struma River. First Sarrail's Russian troops, then some of his French forces mutinied.
Sarrail was able to restore order, aided by the fact that his troops were not aware of the simultaneous mutinies that had assumed more dangerous proportions on the western front. He retained his position only by virtue of his political links; his military record was badly tarnished. In the summer of 1917 the British began to remove two divisions from Salonika. In November Georges Clemenceau became France's prime minister. He was technically a member of the party that had supported Sarrail for years, but their personal relations had never been cordial. Clemenceau's attack on defeatist elements in France sealed Sarrail's fate; investigations in France uncovered documents from Sarrail's headquarters in the hands of known German collaborators. Sarrail was relieved of his command and recalled to France in December 1917. He had no further military role to play in the war.
Sarrail ran unsuccessfully for the National Assembly in 1919, then occupied himself as a journalist and lecturer of the political Left. In the national elections of 1924, his old political supporters returned to office and he went back on active duty. He became high commissioner in Syria and Lebanon, but his failure in dealing with armed revolts led to his recall
in 1925. He returned to private life and died in Paris on March 23, 1929.