Yumashev was born on in Saint Petersburg. After graduating from school he went on to attend art school, and briefly worked as a land surveyor in summer 1918 before joining the Red Army in August that year. Before entering combat of the Russian Civil War he trained as a cadet at the 2nd Petrograd Artillery Course, and in October 1920 he was deployed to the front of the war as part of an artillery division on the Southern Front, where he participated in battles against the forces of Pyotr Wrangel and Nestor Makhno. In February 1921 he departed from the frontlines to attend additional artillery courses in Sevastopol; after graduating he was briefly being stationed in the Kharkhov Military District.
