The PSP originated as the Pro-Independence Movement (Movimiento Pro-Independencia, MPI), founded on January 11, 1959, in the city of Mayagüez. The MPI was formed by a group of dissidents from the Puerto Rican Independence Party (PIP). Over the following years the group was greatly influenced by the Cuban Revolution. During the 1964 elections, the MPI promoted a boycott, and throughout the decade campaigned against the presence of US corporations on the island.
At its Eighth General Assembly on November 28, 1971, the MPI renamed itself the Puerto Rican Socialist Party and endorsed Marxism-Leninism. Juan Mari Brás was named the PSP's general secretary, and Carlos Gallisá Bisbal later became party president. The party gained a following in the labor movement, student movement and community organizations. The PSP was also an observer organization of the Non-Aligned Movement.
PSP branches also emerged in the United States beginning in 1973, most prominently in the Puerto Rican neighborhoods of New York City and Chicago. One of its most prominent leaders in the US was Luis Gutierrez, who later became a Chicago alderman in the 1980s and a US Congressman in the 1990s. The PSP was primarily responsible for a pro-independence rally that drew 20,000 people to Madison Square Garden on October 27, 1974. PSP members were also active in the movement against the Vietnam War.
The PSP faced disruption from the FBI's COINTELPRO program and attacks from anticommunist forces on the island. Mari Brás's son, Santiago Mari Pesquera, was murdered mysteriously in March 1976, and the offices of the PSP newspaper Claridad were bombed. Several party members narrowly escaped murder attempts.
Disagreements arose within the party over whether to engage in guerrilla warfare or to enter electoral politics. After a poor showing in the 1976 elections, these disagreements over tactics paralysed the PSP. The party's membership and following declined in the 1980s, and it formally disbanded in 1993. However, Claridad continues to be published as a weekly newspaper. Mari Brás and other former PSP leaders later became involved in the Hostosian National Independence Movement (MINH).
On May 5, 2007 at Hostos Community College in the Bronx, NY, former members of the PSP, now working under the name of the October 27 Committee, held a small conference on, "Desde Las Entrañas 30 Years Later: Implications for the Independence Movement." Desde Las Entranas was the political declaration of the First Congress of the United States Branch of the Puerto Rican Socialist Party, approved on April 1, 1973. This 77-page document, examined, "the nature of Puerto Rican immigration to this country; its present composition, its attitudes and behavior, its experience within the system of exploitation imposed by the ruling class of this country, the relationship between its working class and the exploited countries of the Third World, the super-exploited sectors of this country and their role; the nature of national liberation struggles and their relation to the class struggles of the United States working class; the future that this system assigns to our youth and, finally, the present situation of the left in the United States." (1976 translation) Organized by José "Che" Velazquez, speakers at this 2007 conference included Andres Torres, Raquel Rivera and Angelo Falcón.
- Andrés Torres and José E. Velázquez (eds.), The Puerto Rican Movement: Voices from the Diaspora (Temple University Press, 1998) ISBN 1-56639-618-2
- Max Elbaum, Revolution in the Air: Sixties Radicals turn to Lenin, Mao and Che (Verso, 2002) ISBN 1-85984-617-3
- Manuel Maldonado-Denis, "Prospects for Latin American Nationalism: The Case of Puerto Rico," Latin American Perspectives 3:3 (Summer 1976).
- Puerto Rico: The Last Colony International Socialist Review.