[citation needed] The aim of the party's founders was to offer voters a moderate alternative to Fretilin and UDT.

The PSD was one of five parties in the Alliance of the Parliamentary Majority (AMP) coalition in Timor-Leste's national parliament, which formed the government between 2007 and 2012.

The Party (PSD) was established by Mario Viegas Carrascalao,[2] Zacarias Albano da Costa, and Leandro Isaac, amongst other prominent figures of the timorese political elite on 20 September 2000.

The Social Democratic Party is currently led by Zacarias Albano da Costa, who is also Minister for Foreign Affairs since 8 August 2007.

In the first parliamentary elections on 30 August 2001, the PSD received 8.2% of the vote, giving it six of the 88 seats in the East Timorese parliament.

Milena Pires (former campaign manager of Xanana Gusmão, gave up her mandate to become head of UNIFEM Timor-Leste) and Mário Viegas Carrascalão were replaced during the legislature by João Mendes Gonçalves and Maria da Paixão da Costa, the vice-president of Parliament.

At the beginning of March, Isaac joined the rebels trapped in Same, led by Alfredo Reinado, to protest against their imminent arrest.

Later, party leader Mário Viegas Carrascalão announced his candidacy, but then Lúcia Lobato stood as the only female candidate in the elections.

In the parliamentary elections on 30 June 2007, the PSD ran in a joint list with the Timorese Social Democratic Association (ASDT).

In which, the President of the Social Democratic Party is currently led by Zacarias Albano da Costa, who is also Minister for Foreign Affairs since 8 August 2007.

[5] The PSD then joined the Fórum Demokrátiku Nasionál (FDN),[6] but in 2018, before the early new elections on 12 May, it separated from the alliance to become part of the Movimento Social Democrata (MSD).

In the 2018 early general elections in Timor-Leste, the MSD failed significantly to clear the four percent hurdle with only 3,188 votes (share: 0.5%).

Costa was East Timor's foreign minister between 2007 and 2012, formerly an adviser to the US Department of Development USAID and a former deputy chair of the UDT (1993-2000).

Papito Monteiro was Secretary of State for Rural Development from August 2007 to September 2008, but resigned from his post for health reasons.