Leon Kovarskii was born in 1927 in Chișinău (Kishinev), Romania (present-day Moldova). His father Samuel-Chaim, a native of Lithuania, worked as a teacher at various Jewish educational institutions. In 1935, the family moved to Lipcani, northern Bessarabia. In June 1940, Bessarabia was annexed to the Soviet Union, and the Kovarskiis became Soviet nationals overnight. On the day when the Soviet-German war began, Leon was in a pioneer (scout) camp close to the new Soviet-Romanian border. Reluctant to return under the rule of the quasi-fascist Romanian regime, Leon and a group of teenagers from the camp fled eastward. Following an arduous trek, they arrived in Stalingrad, on the Volga River, and were admitted into an orphanage. His father, stepmother, and sister remained under German-Romanian rule. In 1942, the orphanage was transferred to Perm, northeastern Russia, where the adolescents were distributed among the local vocational schools.
In 1943-44, the 16-year-old Leon, tired of the permanent starvation in Perm, volunteered for the Red Army. He was accepted as a rifleman into the 89th Separate Transport Company of the 8th Rifleman Division; his duty was to guard transports that supplied the division with ammunition. With this division, Kovarskii fought in Eastern Galicia (present-day Ukraine), Carpathian Ruthenia, and Slovakia. In late 1944-45, he was transferred to the reserve 254th Tank Brigade; his duties included receiving new vehicles for the brigade at the Sormovo tank plant (in central Russia). He ended the war in Poland.
Sergeant Leon Kovarskii was discharged from military service in December 1946, and returned to Kishinev. All of his family had perished during the occupation. Having no employment or residence in the city, he found an administrative job in the Chernivtsi (Czernowitz) region, Ukraine, near Bessarabia. In parallel, he obtained a degree from Czernowitz University, and worked as a history teacher until 1992. In 1953, he attempted to defend a candidate (PhD) thesis, but failed because of the Stalinist anti-Jewish campaign. Only in 1977 was he able to defend his thesis in Moscow.
In the late 1990s, Leon Kovarskii immigrated to Israel. He has been active in local associations of World War II veterans.