Leontii Shapiro was born in 1926 in Zaporozhie, Ukraine, as the third of six children. His father Boris was a horse carter. The family was poor, and they lived in a basement apartment. From the age of 8, Leontii had to work to support the family: He sold homemade cakes at the local market. Later, he and his younger brother sawed and chopped firewood for their more affluent neighbors. Nevertheless, Boris sent all his children to schools and wished to give them an education. Upon finishing school, Leontii entered a vocational school, intending to become a factory worker.
In June 1941, the Soviet-German War broke out. In August 1941, the Wehrmacht approached Zaporozhie, and the Shapiros tried to evacuate, but failed to do so (their horses were seized by the military). Leontii's father Boris, his older brother Moisei, and his sister Asia (Khasia) were drafted into the Red Army, while the rest of the Shapiro family remained in Zaporozhie, which was occupied by the Germans in the first days of October 1941.
Leontii Shapiro managed to survive the two-year-long German occupation of Zaporozhie and the surrounding area. He evaded the first mass-murder of the Jews of Zaporozhie in March 1942, while his three younger siblings were killed in the spring of 1942, and his mother hanged herself. Leontii's Ukrainian neighbors provided him with forged "Aryan" documents, and, under the alias of Levko Shcherbina, a Ukrainian, he left the city for a nearby village, where he worked as a farmhand. On two occasions, the Germans drafted him, along with other Ukrainian youths, for forced labor in Germany, but in both cases, he was able to escape from the transport and return to the village.
In September 1943, the Red Army entered the village where "Levko Shcherbina" lived. Leontii immediately asked the Soviet commanders to let him join the regiment, arguing that, since all the villagers now knew that he was Jewish, he might be killed at any moment; besides, his father and two siblings were serving in the Red Army. The commanders agreed, and Leontii joined the unit as a "volunteer". Despite not being registered as a soldier, Leontii was given a rifle, with which he took part in the fighting on the way to Zaporozhie. He then participated in the liberation of the city in October 1943. After the liberation, his commanders dismissed him from the army as being too young ("Be free, lad, for another year," they told him). Shapiro moved back into his former apartment. A short time later, he was arrested by the NKVD (political police), who wanted to know how he, a Jew, had managed to survive in an occupied area. After two weeks of interrogations, Shapiro was released. In late 1944, he was drafted and sent to a sergeant school. He finished it, but was unable to take part in combat, because the war was over by that point. Nevertheless, he went on to serve in the army until 1949. Throughout his term of service, he kept the name "Leonid Shcherbina", and only after his discharge did he restore his original last name, Shapiro.
Leontii's father Boris was taken prisoner by the Germans a few days after being drafted into the Red Army. Following a quarrel with another POW – an ethnic Roma who used to be a horse carter, like Boris – he was denounced by the former as a Jew and shot by the Germans. Leontii's brother Moisei served with the tank forces and ended the war in Germany. His sister Asia also survived the war.