Founded under Francoism, it merged into the Spanish Socialist Workers' Party shortly after the 1977 general election.

The origins of the party dated back to 1954 when the university professor Enrique Tierno Galván published various academic studies of a Marxist character.

[1] In 1965, working with Raúl Morodo, he formed the Castillian Socialist Federation (Federación Socialista Castellana).

[1] In Francoist Spain, it was an illegal underground movement on university campuses, and it adopted the Popular Socialist Party name in 1974.

[1] In contrast to the PSOE, which had a base in the trade union movement, many PSP members were university professors and intellectuals.