Founded on 23 August 1963 with the intention of forming a nationalist and social democratic party in Galiza, subsequently radicalized its positions, approaching the communist Galician People's Union (UPG).

The new party attracted former members of the Partido Galeguista as Francisco Fernández del Riego, who was elected party president, Luis Viñas Cortegoso, Amado Losada, Domingo Pombo and young influenced by Ramón Piñeiro like Xosé Manuel Beiras or Ramón Lugrís.

The poor results of the general elections of 1977 and the PSOE pressures caused the rupture of the FPS, and the PSG entered in a severe crisis.

This group organized the Socialist Collective-PSG led by Xosé Luis Rodríguez Pardo, Ceferino Díaz and Fernando González Laxe, that had around 100 militants.

This decision to approach the BNPG caused a strong discontent within the PSG and many militants left the party after this congress.