After Operation Barbarossa began, Beylin was released from the academy in July 1941 and placed at the disposal of the Military Council of the Northwestern Front, where he was appointed senior assistant chief of the operations department of the staff of the 27th Army. In this position, he fought in defensive battles on the Western Dvina, on the Velikaya on the line of Vybori and Opochka, and on the Lovat in the area of Kholm. In August the army fought in the Staraya Russa counterattack. Subsequently, its units fought in defensive battles in the Demyansk sector and by the beginning of October halted the German offensive on the line of Lake Velye and Lake Seliger. From 14 January 1942, then-Lieutenant Colonel Beylin served as deputy chief of staff of the 4th Shock Army, which fought in the Toropets–Kholm offensive as part of the Kalinin Front. Between 18 May 1942 and September 1943, he was chief of staff of the 2nd Guards Rifle Corps on the Kalinin Front, part of the 3rd Shock, 22nd, and 29th Armies. Then-Colonel Beylin served as temporary corps commander between 29 September and 24 October 1942, leading it in battles in the Nevel sector as pat of the 3rd Shock Army. Between November 1942 and January 1943, the corps fought in the Velikiye Luki Offensive.