Sapronov was born in Mostaushka, Tula Governorate in a family of Russian ethnicity. Whilst working as a house painter Sapronov joined the Bolshevik faction of the Russian Social Democratic Labour Party in 1912. He was active during the Russian Revolution and Russian Civil War in the Moscow Provincial Soviet. Sapronov was a left communist of the Bukharin group in 1918. From October 1917 to December 1919, he was the chairman of the Moscow City Executive Committee, after which he was sent to Kharkov and liberated it from Anton Denikin's troops. in 1920 he became the chairman of the Kharkov provincial revolutionary committee and the executive committee. Sapronov, with other Moscow Communist Party left-wingers Vladimir Smirnov and Valerian Obolensky-Ossinsky, he initiated the inner-party grouping known as the Group of Democratic Centralism which presented its case at the Eighth Party Congress in 1919 that 'the party should not impose its will on the soviets’. However it obtained only a derisory number of votes and was denounced as semi-syndicalist by Vladimir Lenin.