Gallwitz volunteered for the war against France in 1870 and later served in the General Staff as well as the Prussian War Ministry; he was promoted major in 1890 and colonel six years later as chief of field artillery in the War Ministry. Gallwitz was promoted major general in 1902 and appointed department head in the War Ministry as well as deputy chief to the German Bundesrat. Three years later, Lieutenant General Gallwitz commanded the Sixteenth Division and in 1911 became inspector of field artillery in the grade of general of artillery. The kaiser raised him into the Prussian nobility in 1913.
Gallwitz entered the Great War as commander of the Guards Reserve Corps as part of the Second Army, and General Karl von Bülow on August 18 ordered him to storm Namur. Thereafter, Gallwitz's Corps was transferred to the east, arriving too late for the battle of Tannenberg but in time on September 9-12 to form the left wing of the Eighth
Army at the Masurian Lakes as it enveloped the Russian Second Army. Next came service with the Ninth Army in Silesia and Poland (Ivangorod), then with Army Group Woyrsch near Cracow, and finally as leader of Austro-Hungarian units at the Pilica River.
On February 9, 1915, Gallwitz became head of an army group bearing his name in southeastern Poland and engaged in heavy fighting near Przasnysz. In July Army Group Gallwitz accompanied Field Marshal August von Mackensen during the latter's campaign in Galicia, and thereafter Gallwitz crossed the Narev River and occupied Pultusk, Rozan and Ostrolenka with a newly formed Twelfth Army; in the process he took 111,111 Russian prisoners of war.
On September 30, 1915, Mackensen placed Gallwitz at the head of the Eleventh Army for the campaign in Serbia. The Germans crossed the Danube on October 7, and by the end of November the greater part of the country had been conquered in conjunction with the Austro-Hungarian Third Army. While planning an assault against the Allies at Salonika, Gallwitz, on March 29, 1916, instead was appointed commander of a special Meuse Group West at Verdun. However, General Erich von Falkenhayn next transferred this veteran commander to the Somme, first as head of the Second Army and later as commander of yet another army group bearing his name (German First and Second Armies).
The new army commanders, Field Marshal Paul von Hindenburg and General Erich Ludendorff, in December 1916, appointed Gallwitz head of the Fifth Army before Verdun with the task of stabilizing this sector after the French had retaken Fort Douaumont. In January 1918, Gallwitz's Fifth Army was reinforced with Army Division C and reconstituted as Army Group Gallwitz to the end of the war. In this capacity, Gallwitz absorbed the brunt of American charges in the Meuse-Moselle theater in the fall of 1918. Specifically, his forces blunted the American thrust into the St. Mihiel salient and held the fortified Michel line. The general counseled against an armistice early in November, and instead called for an appeal to the nation to rally in defense of the homeland. Gallwitz resigned on December 6, 1918; from 1920 to 1924 he served in the Reichstag as deputy for the German National People's party.
Gallwitz on several occasions narrowly missed higher appointments. Before the war he had been considered for the posts of Prussian war minister and chief of a military mission to Turkey; from 1914 to 1918 he was twice mentioned as a possible chancellor, and in November 1918, he almost became Hindenburg's successor. These honors attest to his self-confidence, education, and great sense of duty. Gallwitz died in Naples on April 17,1937.
In 1891, he married Friedrike. They had a daughter and son Werner, who became a Lieutenant general in the Second World War.