Yuriy was born in Yuryev, Governorate of Livonia, into a family of a book publisher Vladimir Sablin (1872-1916) and daughter of the Russian playwright Fyodor Korsh, Varvara.
During the World War I, in 1916 Sablin volunteered to army and served in artillery as a battery sergeant (vice-fireworker).
After his recovery in a hospital, Sablin graduated the 2nd Moscow school of ensigns in 1917 and then served in the 56th Reserve Infantry Regiment.
Since March 1917 Sablin was a member of Left Socialist Revolutionaries and the Moscow city Council Ispolkom.
By the end of the Russian Civil War, Sablin finished the Military Academy and Higher academic courses in 1923 and pilot school in 1925.