The PPS was founded in December 1919 by Egisto Morri, Carlo Balsimelli and some socially engaged priests.
During midsummer 1920, the PPS organized some farmers' strikes and called for general elections, which took place on November 14, 1920.
However, the revolutionary, and finally self-disruptive, political line of the Socialists, which abandoned the Grand and General Council to organize continuous strikes, left the Populars alone against their other opponents, the rightist Sammarinese Democratic Union which was led by the new-born Sammarinese Fascist Party.
Benito Mussolini's agents worked to lead the small republic toward a dictatorship.
The PPS was finally disbanded by the Fascists in 1925, a few days after the closure of the PPI in Italy.