Marxist-Leninist/Socialist party which dominated Santomean political life as the nation's sole political party from the country's birth in 1975 until 1989, when the nation opened up to multi-partyism. A switch in party leadership in 1974 inspired by Portugal's April 25, 1974 Carnation Revolution turned the party sharply into the Soviet sphere. Party maintains very close relations with Communist China.
Reformers at a 1990 MLSTP party congress forced the party to democratize, renaming itself the Movement for the Liberation of São Tomé and Príncipe/Social Democratic Party (MLSTP/PSD). Party is led by Aurélio Pires Quaresma Martins. Attorney and Principean politician Guilherme Pósser da Costa was the MLSTP/PSD's candidate for President of São Tomé in 2021 [Movimento de Libertação de São Tomé e Príncipe/Partido Social Democrata (MLSTP/PSD)].
