In August 1941, Varennikov was drafted by the Armavir city military registration and enlistment office into the ranks of the Red Army. He attended the Cherkassk Infantry School, which was then evacuated to Sverdlovsk following the start of Operation Barbarossa. From October, the first military recruitment began to train. After an accelerated graduation from the school in the summer of 1942, Varennikov was among the few graduates to be appointed the commander of a training platoon in the reserve rifle brigade stationed in Gorky, and only in October 1942 he ended up on the Stalingrad Front as commander of a mortar platoon of 120-mm regimental mortars of the 138th Rifle Division. He fought in the Battle of Stalingrad for 79 days and nights. In November 1942, Varennikov was appointed battery commander, and in December of the same year he participated in the destruction of the encircled units of the German 6th Army commanded by Field Marshal Friedrich Paulus.