Groener entered the Württemberg Army and rose through the ranks, completing the Kriegsakademie at the head of his class in 1896, ahead of Hans v. Seeckt. Transferred to the Great General Staff, he served later as a popular instructor at the Kriegsakademie.
When Moltke the Younger became Chief of Staff in 1905, he deliberated long over the key post of chief of operations. His two candidates, recognized as the brightest in the army, were Ludendorff and Groener. The position went Ludendorff who had slightly better family connections. Groener had to settle for the transport section, a vital post. He later opposed Moltke's and Ludendorff's changes to the Schlieffen Plan which consisted of weakening the ratio of the strong right wing in favor of the weak left wing.
Nonetheless, when war came, the transport of the newly mobilized forces to the various fronts functioned flawlessly. Taking advantage of Germany's interior lines of communication and superb rail network, Groener kept men and materiel moving smoothly to the armies in the field. The Kaiser recognized his service with the Pour le Mérite in 1915.
Promotion to brigadier came in 1915, followed by a new position in May of 1916, as head of the Army Food Supply Office. The length of the war and the increasingly effective English naval blockade necessitated a drastic reorganization of the German economy. The High Command took over the economy with the imposition of its new economic reorganization, the Hindenburg Program, in late 1916. Now a Major General, Groener headed this program from a new agency, the War Office. His ability to deal with people led to a truce with the various labor organizations whose leaders recognized that Groener was fair and kept his word. While not a democrat by any means, he recognized that labor was an equal partner in the economy. Trying to balance the incompatible demands of the increasingly voracious war machine for men and materiel with the equally importunate needs of the economy for the same commodities, his methods estranged the High Command. Ironically, under his leadership the army largely established the principle of collective bargaining for labor and paved the way for the alignment of the army with Social Democracy in the early years of the Weimar Republic. His success incurred Ludendorff's jealousy, and when Groener tried to curb the excessive profits of heavy industry, the Quartermaster General arranged for Groener's transfer to the Western Front. Ostensibly Groener left to command the 33rd Division in August 1917 because he had set up the War Office; in reality, he was sacked. He later took over the XXV Reserve Corps, and in 1918 became commander of the I Corps.
With the signing of the Treaty of Brest-Litovsk in March of 1918, the High Command recognized that Groener was the only general capable of enforcing the economic provisions of the treaty fast enough to benefit Germany. Groener was sent east in April, ostensibly as chief of staff of Army Group Kiev but in reality to organize and head Germany's economic interests in the Ukraine. He remained there until the end of October 1918 when the Kaiser and Hindenburg called him to Spa to replace Ludendorff as Quartermaster General. He arrived hours ahead of the Kaiser who had decided to flee an inhospitable Berlin and just in time to be saddled, in the popular mind, with the armistice.
Groener recognized Germany's impossible position, and he urged the negotiation of an armistice at once--as had Hindenburg and Ludendorff. When Hindenburg shirked his duty at the end, to Groener fell the unenviable task of telling the Kaiser the army no longer stood behind him. At first opposed to the imperial abdication, Groener met in Berlin with Ebert (later President of the Weimar Republic) in early November and became convinced the Kaiser had to go. The Kaiser refused, however, and troops and sailors began to mutiny. Order disintegrated fast, and the specter of a communist revolution and civil war at home loomed.
To preserve the unity of Germany Groener and Ebert struck a deal: the army would assist a republican government in maintaining law and order provided that government respected private property and the social order. Informed by Groener that he no longer enjoyed the confidence of the army, the Kaiser dithered, but the Socialists in Berlin did not wait for a reply, declaring a German Republic the morning of 9 November. The Kaiser fled to Holland the morning of 10 November.
Groener remained on active service, trying to keep the army out of the armistice and peace negotiations, hoping that it could avoid blame for what he knew would be harsh terms. In this he succeeded, but he could not live up to his part of his pact with Ebert. When unrest and finally revolution broke out in January 1919, the army could not muster sufficient forces to restore law and order in Berlin. The new Ebert Government had to resort to using temporary volunteers (Freikorps), whose brutal excesses alienated the working classes. Nonetheless, the Communist-Sparticist revolution was crushed. In the fall of 1919 Groener retired, but he came back a year later and served as Reich Minister of Transport until 1923. Once again, however, he answered Hindenburg's call when the aged president asked him to serve. From 1928 until 1932 Groener served as Defense Minister (Reichswehrminister) and Interior Minister (1931-32). He kept the Nazis out, while at the same time taking steps that permitted Hitler's rapid expansion of the Reichswehr into the Wehrmacht. Declared persona non grata by the Nazis, he lived quietly in retirement until his death in 1939.
Groener's edited memoirs were published in 1957, Lebens-Erinnerungen: Jugend, Generalstab, Weltkrieg.
His daughter is his biographer: Dorothea Groener-Geyer, General Groener: Soldat und Staatsmann, 1955.
A 1977 work by G. Rakenies, Groener Als Erster Generalquartiermeister...1918-1919, chronicles that period.
His papers exist in the German Military Archive, now back in Potsdam.