On 26 January 1957 the PSP was founded by the Action group. The first year was devoted to the organisation of the party and the preparation for the elections which were expected to be in 1960. The party sought to expand its membership, its branches and its electoral support. The founders were joined by members of the Socialist Union, a group which had split unsuccessfully from the PvdA in 1950. In 1958 it entered in the provincial elections and it won two seats in the North Holland provincial legislative. In the 1959 elections the party won two seats in the House of Representatives.