[1] After graduation from the humanistic Gymnasium in Regensburg, on 12 August 1888 Hemmer entered the Royal Bavarian 11th Infantry Regiment "Von der Tann" (Königlich Bayerisches 11.

Hemmer served as a battalion adjutant in that regiment from 15 February 1893 to 1 June 1896, after which he was sent for 3 years of general staff training to the Bavarian War Academy.

On 20 October 1907, he was named a company commander in the Royal Bavarian 8th Infantry Regiment "Grand Duke Friedrich II of Baden" (Königlich Bayerisches 8.

[1] On 30 November 1914, he was promoted to Oberstleutnant (lieutenant colonel) and on 28 December 1914, he was named chief of the general staff of the I Royal Bavarian Reserve Corps.

In recommending him for the Commander's Cross of the Military Order of Max Joseph, Graf von Bothmer cited him "for his outstanding merits, characterized by exceptional intelligence, energy and tireless perseverance, in the preparation and successful execution of the challenging defensive battles during the Russian summer offensive of 1916.

He was awarded the Order Pour le Mérite, Prussia's highest military honor, on 25 August 1917, and was promoted to Oberst (colonel) on 14 December 1917.

[1] The 19th Army was demobilized on 18 December 1918,[4] and in January 1919, Ritter von Hemmer was again named a statutory member of the Bavarian Senate of the Reichsmilitärgericht (Reich Military Court).