Movement for the Liberation of São Tomé and Príncipe – Social Democratic Party

The party, then called the Committee for the Liberation of São Tomé and Príncipe, was founded in 1960 as a nationalist group opposed to Portuguese colonial rule. In 1961 it joined the CONCP with other communist and socialist groups fighting against the Portuguese Empire in Africa. The CLSTP was set up by exiles who eventually established their base in nearby Gabon. Manuel Pinto da Costa, who would eventually become President of an independent São Tomé and Príncipe, was the leader of the party. In 1972, the CLSTP became the MLSTP.

After the April 1974 Carnation Revolution in Portugal, the new government agreed to hand over power to the MLSTP. Later that year, the MLSTP was recognized as the sole legitimate representative of the Santomean people.

Following a brief period of transitional government, elections were held for a constituent assembly and the MLSTP won all 16 of its seats.

Independence was achieved on 12 July 1975, with Manuel Pinto da Costa as president and Miguel Trovoada as Prime Minister. The constitution promulgated on 12 December 1975, effectively vested absolute power in the President and the MLSTP became the nation's sole legal political party.

During the late 1970s and 1980s, the party's socialist orientation and in turn the nation developed strong ties with Cuba, East Germany and the Soviet Union.

In late 1989, a progressive faction within the party embarked on a transition to full multi-party system, after a debate at the national party conference.

A democratic constitution introduced by the MLSTP Central Committee was approved overwhelmingly in an August 1990 referendum.

At the MLSTP Party Congress in October 1990, Carlos Graça was appointed as the new Secretary-General, in succession to Manuel Pinto da Costa. In addition, the party's name was amended to the Movement for the Liberation of São Tomé and Príncipe – Social Democratic Party (MLSTP–PSD).

In an extraordinary Congress of the MLSTP–PSD held in May 1998, Manuel Pinto da Costa was elected unopposed as President of the party, a post that he held until 2005.

At the party's Fourth Congress, Guilherme Posser da Costa, a former Prime Minister, was elected as President of the MLSTP–PSD on 27 February 2005, succeeding Pinto da Costa. There were 708 votes in favor of Posser da Costa, who was the only candidate, and three votes against him.[2] As of June 2008, the President of the MLSTP–PSD is Joaquim Rafael Branco.[3]

In June 2008, after Prime Minister Patrice Trovoada of the Independent Democratic Action (ADI) party was defeated in a vote of no confidence, President Fradique de Menezes asked the MLSTP–PSD to form a government, and it chose Branco to become the next Prime Minister.[3] The ADI denounced Menezes' designation of the MLSTP–PSD to form a government as unconstitutional, arguing that it was too late in the parliamentary term to do so, and it took the matter to the Supreme Tribunal of Justice.[4]

The current president of the MLSTP–PSD, Aurelio Martins, was elected on 15 January 2011 in the V Ordinary Congress of the Party.

Today the MLSTP–PSD has friendly relations with political parties in other Lusophone countries, including the Socialist Party (PS) in Portugal and the People's Movement for the Liberation of Angola (MPLA).