Oleksandr Liashko was born into a family of a railway worker in Rodakove, located in present-day Luhansk Oblast, eastern Ukraine.
After graduating from the school in 1942, he received the rank of lieutenant and was assigned to the Gorky Automobile Plant, which had begun producing tanks.
The platoon commanded by Liashko received combat vehicles and was transferred to the North Caucasus Front.
After organizing effective repairs of military equipment in 1943, he returned to the tank school, where he taught special subjects until the end of the war.
Starting in 1945, Liashko worked as an engineer in the open-hearth shop at the Novokramatorsk Machine-Building Plant in the Stalin Region.
Concurrently, he continued his studies at the Donetsk Industrial Institute, graduating in 1947 with a degree in metallurgical and mechanical engineering.