Myachin was awarded the title Hero of the Soviet Union for his leadership of a battalion during the Berlin Offensive.

Postwar, Myachin continued to serve in the army, retiring in 1978, after which he worked as an air traffic controller.

Myachin was born on 19 December 1918 in the village of Soldatskoye (now in Terbunsky District, Lipetsk Oblast) to a peasant family.

On 20 and 21 April, the battalion was reported to have killed 400 German soldiers, destroyed eighteen emplacements, and knocked out four self-propelled guns and a tank.

During fighting on 22 to 23 April, near Kołbaskowo, Myachin was reported by his superiors to have personally led his battalion seven times in the attack against the German strongpoint.