Leontii (Leon, Leyb) Kotliar was born in 1901 into a Jewish family that lived in the Russian city of Tomsk in Siberia. His father worked as a tinsmith at a railroad depot. In 1902 the family moved to another Siberian city, Kansk. Leontii lived there until 1920, when he volunteered for the Red Army. By that time he had completed a science-oriented high school. After that he graduated from the Petrograd Military Engineering School and in 1930 the Military- Engineering Academy. In 1937 and 1938 he served as a quality-control engineer in the People's Commissariat of Defense of the USSR. In September 1939, as head of a unit of engineering forces of the headquarters of the Ukrainian Front, Kotliar took part in the Soviet annexation of western Ukraine, which had been part of eastern Poland.
In June 1940, when the Red Army introduced different ranks of general, the 39-year-old Kotliar was made a major-general of engineering forces. At that time he was a general inspector of the engineering forces of the Red Army.
During the first, most difficult period of the Soviet-German war, when Wehrmacht troops threatened Moscow, Kotliar was head of the engineering forces of the Red Army and was in charge of the construction of defense installations around Moscow. On February 21, 1942 he was awarded the Order of Lenin for this work.
However, in April 1942 Kotliar was replaced as general inspector of the engineering forces. From September of that year he served in the regular army, first as head of the engineering forces of the Voronezh Front then, in 1943, of the South-West Front and, finally (from 1943 to 1945), of the 3rd Ukrainian Front.
On March 19, 1943 Leontii Kotliar was promoted to lieutenant-general and, exactly one year later, to colonel-general. On November 8, 1944, the article "Colonel-General of the Engineering Forces Leon Kotliar," by Shmuel Persov was published in Eynikayt, the newspaper of the Jewish Anti-fascist Committee.
The troops with which he fought took part in the liberation of the Donbas, in the fighting at the Dnieper River, and in the liberation of Moldavia, Romania, Hungary, Bulgaria, Austria, and Yugoslavia.
On April 28, 1945 Colonel-General of the Engineering Forces Kotliar was awarded the title of Hero of the Soviet Union.
In September of that year he became head of the Military-Engineering Academy, from which he himself had graduated in 1930.
Kotliar died in December 1953.