Marwitz was assigned to the Western Front in 1914 as commander of II Cavalry Corps, and participated in the Battle of Haelen. After this first battle Marwitz was transferred to the Eastern Front to take command of the newly formed XXXVIII Reserve Corps, which he led in the Second Battle of the Masurian Lakes in the early winter of 1915. He was then transferred south and fought with Austria-Hungary against the Russians and was awarded the Pour le Mérite on 7 March 1915.