Efim Mazler was born in 1923 in the village of Zhabokrych in southwestern Ukraine, near the border with Moldavia (Moldova), as Froim (Efraim) Mazler. He was one of eight siblings. His father Asher was a glazier; his mother was a homemaker. The parents were religiously observant, while the children were less so. In 1931, Asher Mazler joined a kolkhoz.
In June 1941, the Soviet-German War broke out; Efim and his parents failed to evacuate and remained under Romanian occupation. His father was randomly killed by the Romanians during the first days of the occupation. Efim, his mother, and sister survived the Kryzhopil Ghetto. His brother Isaac died of tuberculosis in the ghetto in the summer of 1941. His sister Mala, who lived in Odessa, was murdered together with her baby. Two brothers of his were killed in action. Two other siblings, who had gone away before the war, survived.
In early March 1944, the area was liberated by Soviet troops. On March 15, Efim Mazler was drafted into the Red Army. Two days later, without receiving adequate training, he was sent to the frontline and attached to the 656th Rifle Regiment of the 116th Rifle Division. He saw action in Bessarabia and crossed the Pruth River in Sculeni. In August 1944, he took part in the Jassy–Kishinev Offensive of the Red Army, after which his division was transferred to the Sandomierz bridgehead in southern Poland. He then participated in the takeover of Stettin. He was wounded, and discharged from the army in 1946. In the course of the war, Efim Mazler was awarded the Order of Glory, 3rd class (for his part in crossing the Pruth River), and some medals.
Efim's brother Aron Mazler (born in 1911) was drafted in Kryzhopil on the second day of the Soviet-German War. He took part in the Stalingrad Operation in 1942-43. His last place of service was the 757th Rifle Regiment, on the 3rd Belorussian Front, where he served as a mortar gunner. Aron Mazler was killed in action on April 26, 1945. Another brother of Efim, Nusya Mazler (born in 1912), was drafted into the Red Army in May 1941, a month before the German invasion of the Soviet Union. According to family legend, he was taken prisoner by the Germans in 1944, denounced as a Jew by his fellow POWs, and killed.
In 1946, Efim Mazler returned to Kryzhopil. He lived in Bolgrad near Odessa, and later moved to Balta. After the war, he worked in administrative positions.