In 1917, Russia the Socialist-Revolutionary Party split between those who supported the Provisional Government, established after the February revolution, and those who supported the Bolsheviks who favoured a communist insurrection.

The majority stayed within the mainstream party but a minority, who supported the Bolshevik path became known as Left Socialist-Revolutionaries. They in effect split from the main party and in the election to the Constituent Assembly often stood as left-SRs against the mainstream party (although with little electoral success).

Many left-SRs joined the Soviet government after the Bolshevik revolution of October, 1917, although those that did resigned their positions in protest at the signing of the Treaty of Brest-Litovsk. The left-SRs were implicated in the assassination of the German ambassador to the Soviet Union.

Some left-SRs became full members of the Communist Party of the Soviet Union.