After graduating from a commanders' school, he held staff positions during the 1920s and early 1930s in Central Asia before transferring to the emerging mechanized forces.

Postwar, Mitrofanov served in armored forces staff positions and ended his career as an advisor to the East German National People's Army.

In this capacity, Mitrofanov participated in the Soviet invasion of Poland before entering the Military Academy of the General Staff in December 1939, from which he graduated in 1941.

[4] After Operation Barbarossa began, Mitrofanov was placed at the disposal of the commander-in-chief of the Northwestern Strategic Direction, and in September appointed chief of the Armored Forces of the 55th Army of the Leningrad Front.

Mitrofanov led the corps in successful attacks during the Lvov–Sandomierz Offensive, in which it captured Gorodok and Lvov, and fought in battles for the Sandomierz bridgehead.

In April, during the latter, Mitrofanov, leading from the front, commanded the corps in its breakthrough of the German defenses on the Neisse and the fortified point of Gross Bademeisel, south of Forst, and the crossing of the Spree.

[4] Hero of the Soviet Union citation During the operations of the army to take the city of Berlin from 16 April 1945, Comrade Mitrofanov, commanding the corps, proved himself to be a bold and decisive general.

The units of the corps, led by Comrade Mitrofanov, broke through the strongly fortified and deeply echeloned German defenses on the Neisse river, forced the Spree river, and rapidly advanced, breaking through the strongly fortified defensive lines on the approaches to Berlin, capturing the cities of Vetschau, Lübbenau, Golssen, Baruth, and Zossen.

For [his] skillful and courageous leadership and the successful combat operations of the units of the corps upon entering the capital of Germany, the city of Berlin, inflicting heavy losses in manpower and equipment on the enemy, for courage and heroism displayed in the fighting, Comrade Mitrofanov [is] worthy of the title Hero of the Soviet Union with presentation of the Order of Lenin and the Gold Star Medal.