On 22 June, Germany invaded the Soviet Union in Operation Barbarossa. The corps fought in the Battle of Białystok–Minsk. The corps was not yet fully formed and was at cadre strength. Between 22 and 27 June the corps fought in battles in the Minsk area, unsuccessfully attempting to stop the German advance towards the city. On 26 June it was ordered to conduct a counterattack with the 4th Airborne Corps at Slutsk. The corps attacked with its 93 outdated light tanks and the 4th Airborne Corps advanced on foot instead of conducting an air assault due to a lack of transport aircraft. Both units were unable to stop the German advance. On 30 June the SvislochRailroad Bridge, defended by the 4th Airborne Corps, was captured by the 4th Panzer Division, cutting off most of the 20th Mechanized Corps and a 4th Airborne Corps brigade. The corps and other remnants of Soviet units delayed the advance of the XXXXVI Motorized Corps with their resistance.
Defense of Mogilev
By 1 July it was part of the 13th Army. On 7 July the corps included about 12,000 men with 27 guns and no tanks. From 9 to 27 July it fought in and was destroyed in the Mogilev pocket. By the end of 15 July the corps was defending Mogilev alongside the 61st Rifle Corps and remnants of several divisions. On 21 July deputy corps commander Major General Nikolai Vedeneyev took command after Nikitin was wounded and evacuated. At this time the corps defended Mogilev's eastern approaches. By 25 July, the Soviet troops in Mogilev were running out of ammunition, food and fuel. 61st Rifle Corps commander Fyodor Bakunin made the decision to withdraw against orders and called a meeting with Vedeneyev and three of the division commanders on the breakout plan. The 20th Mechanized Corps would lead the breakout towards the general direction of Roslavl. That night, the corps began the breakout. In the morning, the corps ran into the German 78th Infantry Division at the village of Samulki. Supported by vehicles from an attached reconnaissance battalion, the corps fought on foot and attacked the German positions. The attack was stopped by heavy German machine gun fire. Bakunin ordered the destruction of remaining equipment and ordered the survivors to disperse and break out in small groups. Between 27 and 28 July the corps broke out of the pocket with 100 to 200 men left. The perechen does not state that the corps was disbanded, although it lost most of its men during the battles in the Mogilev Pocket. The corps last appears on the combat composition of the Soviet Army list for 10 July 1941.