The Left Po'alei Zion party was founded in 1920, when the messianic fervour surrounding the Bolshevik Revolution was at its height. Its fate was no different from that of other revolutionary socialist parties in Europe which did not become part of the Comintern. Most of the founding members of this small and unique body had come from Russia and Poland in the Third Aliya, and were torn between the gospel of the Russian Revolution and awareness of the impending destruction of the Jews of eastern Europe. That inner conflict between Jewish nationalism and revolutionary socialism was never resolved, and, as the Second World War drew nearer, it ended in stalemate.

The annals of Left Po'alei Zion are riddled with schisms and a constant ideological rift between its factions. The party was established as a result of the split within the World Union of Po'alei Zion immediately after the First World War. The issue confronting it was whether to join the Third Socialist International or participate in the Zionist Congress. Remaining faithful to the teachings of Borochov, it embarked on negotiations for joining the Comintern. In 1921 the Comintern rejected the demand to be recognised as an autonomous Jewish party, but this did not prevent party members from defining their political position in accordance with the policy of the Comintern in the period between the two world wars. There was, however, no chance of a proletarian revolution in Palestine.

Two trends emerged within Left Po'alei Zion, and these endured through several schisms and unifications until the end of the Second World War, when the party merged with Ahdut Ha-Avoda.