The PST was founded in 1975 by Rafael Aguilar Talamantes, Graco Ramírez and Juan Ignacio del Valle, though the party did not obtain its official registration until 1979.

[4][5] The PST traced its origins to a faction of the Comité Nacional de Auscultación y Organización (CNOA), led by Rafael Aguilar Talamantes, who believed that the group was too slow in their efforts to organize a political party.

[6] Their first act was to organize the Reunión de Intercambio y Consulta on 24 and 25 March with the aim of uniting the struggles of the working class; the event drew 187 attendees from 14 states.

[7][8] Among them were railway worker unionists, professors, tobacco farmers, journalists and members of the Movimiento de Acción y Unidad Socialista (MAUS).

[9] The attendees agreed almost unanimously on the necessity for a new type of Marxist–Leninist party to serve the interests of the exploited working class, and took on the task of recruiting former revolutionaries and socialist sympathizers from around the country.

[11] Throughout the rest of the year and into early 1975, the group was active in the fieldworkers' and peasants' movements and continued distributing copies of El Insurgente in promotion of their organization.

[15] Like most independent left-wing parties that formed during the 1970s student movement, the PST was not able to obtain legal registry under the strict electoral laws of the time.

[19] In the 1985 midterm elections, the PST gained yet another seat in the Chamber of Deputies, giving it 12 members in the LIII Legislature of the Mexican Congress.

In January 1987, members of the PST proposed changing its name to the Cardenista Party of the Mexican Workers in an effort to move away from President Miguel de la Madrid and the PRI.

[22] However, due to their history of working with the PRI, the PST and the PPS were not invited to join the five political entities (including the PSUM) which merged that April to became the Mexican Socialist Party (PMS).