The party won the1976 general election and formed thefirst constitutional government after the 1974 revolution, withMário Soares as prime minister. However, the government was unstable and fell in 1978. The PS lost the1979 election, but returned to power in1983, forming, with the Social Democratic Party, aCentral Bloc coalition. It lasted two years and in1985, the party was defeated and went back to opposition, remaining there for 10 years and losing the two following general elections. UnderAntónio Guterres, the party won the1995 general election and returned to power, lasting until2002, upon the resignation of Guterres. The party made a comeback and won a historicabsolute majority in the2005 general election under the leadership ofJosé Sócrates. By 2011, the economic crisis led the party to lose the2011 snap election and the party returned to the opposition. Despite losing the2015 election, the party formed an agreement with theLeft Bloc and theUnitary Democratic Coalition and managed to appointAntónio Costa asPrime Minister. Costa remained in office for 9 years, until 2024, and during his term won two elections, the last one, in2022, with an absolute majority. After Costa's resignation, the party narrowly lost the2024 election, thus, returning to opposition. The party again lost the2025 election by a larger margin and even fell to third place in Parliament for first time since it's revolution in 1974.
The Portuguese Socialist Action (ASP) was founded in November 1964, inGeneva, Switzerland, byMário Soares,Manuel Tito de Morais andFrancisco Ramos da Costa. The ASP was founded in exile by several Socialist members as political organizations duringSalazar'sEstado Novo regime were forbidden. In 1964, Mário Soares was elected leader of the ASP and the core principles and values of the ASP were approved.[9]
Inspired byMay 68 events,[10] the Socialist Party (PS) was created at a conference of the Portuguese Socialist Action (ASP) on 19 April 1973, inBad Münstereifel inWest Germany:
The twenty-seven delegates decided to found a party ofsocialism andpolitical freedom, making an explicit reference to aclassless society and withMarxism as a source of principal inspiration. However, seven delegates voted against the idea of creating a party, including Mário Soares' wifeMaria Barroso.
In the1995 legislative election, the PS, then led by the already prominentAntónio Guterres, won a general election for the first time in twelve years, and in the1999 election failed to obtain what would have been a historicabsolute majority for the party by only one MP. In 2001, after a massive defeat in the 2001 local elections, Guterres resigned as prime minister and called for new elections in 2002. The Socialist Party lost the2002 general election by a small margin to the PSD, who formed a coalition government with thePeople's Party (CDS–PP). During this time, it has been argued that the Socialist Party moved towards thecentre and adopted theThird Way.[12][13]
In the early 2000s, the party cleaned up its membership database, resulting in a reduction of registered members from 120,000 in 2001 to 77,000 in 2002.[14]
In 2009, after4+1⁄2 years in power, the PS lost the2009 European Parliament elections to the PSD. However, they won thegeneral election held on 27 September 2009 but failed to renew the absolute majority they won in the previous general election. The PS later introduced and legislatedsame-sex marriage. TheEurozone crisis and financial crisis of 2011 hit Portugal very hard, prompting Sócrates' government to impose harshausterity measures. On 23 March 2011, the entire opposition in Parliament said no to new measures proposed by the government. As a result of this, Sócrates resigned as prime minister and asnap election took place on 5 June 2011. In the elections, the PS suffered a huge setback, with 28.1 percent of the vote, ten points behind the PSD, who formed another coalition government with the CDS–PP. Sócrates resigned as General-Secretary on election night after the PS's worst result since 1987. On 23 July 2011,António José Seguro was elected as Sócrates' successor.
Under the leadership of Seguro, the PS won the2013 local elections making significant gains over the PSD and the Socialists again won theEuropean elections in May 2014 but this time only just. They won 31.5 percent of the vote against almost 28% of the alliance between the PSD and CDS–PP. The result was considered quite a disappointment to many PS members and supporters and on 27 MayAntónio Costa, the then-mayor of Lisbon announced that he would stand for the leadership of the PS.[15] Seguro refused to call a new congress and leadership election and instead called for aprimary election, to be held on 28 September, to elect the party's candidate for prime minister in the 2015 general elections.[16] Costa, being endorsed by the left faction of the party and people likeMário Soares,Ana Catarina Mendes andPedro Nuno Santos, easily defeated Seguro, who was supported by the more moderate and centrist wing of the party, by a 67% to 31% margin.
In the2015 legislative elections, the PS polled a disappointing second place, capturing just 32 percent of the votes against the 38.6 percent of the PSD/CDS–PP electoral alliancePortugal Ahead. Despite the victory of the PSD/CDS-PP coalition, the centre-left and left-wing parties achieved a clear majority in thePortuguese parliament. After the second Passos Coelho cabinet fell in parliament, with the approval of a no-confidence motion, the PS forged aconfidence and supply agreement withLeft Bloc andUnitary Democratic Coalition to support aPS minority government. For the first time in Portuguese democracy, the leader of the second most voted political force became prime minister.
In order to avoid bankruptcy due to mounting debt, in 2017, the party, alongside thePSD, thePortuguese Communist Party,BE and the ecologist partyPEV, voted in favour of abolishing party fundraising limits, thereby opening all Portuguese parties toprivate political donorship, that they are not obligated to disclose.[17][18][19][20] The new proposal was reluctantly approved by the Portuguese president Marcelo Rebelo de Sousa.[21]
Costa led a very successful first term as prime minister with a growing economy, low unemployment, and deficit cuts. Although he led a more left-leaning PS, Costa started to shift the party back to the centre in 2018, something that a younger and more left-wing faction, led by ministerPedro Nuno Santos, contested.[22] In the2019 European elections, the PS won a significant victory by achieving 33.4 percent, against the 22 percent of the PSD. The PS also won theOctober 2019 general election with 36 percent of the votes, against the 28 percent of the PSD, but by a closer margin than expected. The Second Costa cabinet was sworn in on 26 October 2019.
In October 2020, the PS lost power in theAzores region after the Socialists lost their majority in theregion's 2020 October elections. The PS only got 39 percent of the votes, a drop of 7 pp, and 25 seats.[23] The right-wing parties PSD, CDS, PPM, CHEGA, and IL won a majority of one seat over the whole left wing, and a few weeks after the election, they forged a deal that led the PSD to government.[24] As of 2021[update], the PS is now in opposition in both autonomous regions of the country.
For the2021 Portuguese presidential election, Costa endorsed the incumbentMarcelo Rebelo de Sousa, something that made some party members unsatisfied. Former PSMEPAna Gomes, a critic of Costa and a member of the left faction of the party, ran for the presidency, declaring herself the candidate ofdemocratic socialism andprogressivism, stating that she has been disappointed with the leadership of the party for not having an official candidate.[25][26] With the support of the left faction of the party and some more moderate members worried about corruption, Gomes finished in a disappointing second place behind de Sousa, who had many endorsements of party leaders like Lisbon's MayorFernando Medina,Eduardo Ferro Rodrigues, andCarlos César.
The party suffered a setback in the2021 local elections by losing several cities to the PSD. However, the main defeat was the loss of Lisbon to the PSD candidate,Carlos Moedas, who defeatedFernando Medina by a narrow 34 to 33 percent margin.[27] After the local elections, tensions between the PS and its left-wing allies, BE and CDU, led to the rejection of the 2022 budget which forced the calling of a snap election forJanuary 2022.[28] Despite polls predicting a close race between the PS and PSD, the Socialists won a surprise absolute majority, only the second in their history, with 41 percent of the votes against the 29 percent of the PSD,[29] and winning 120 (52%) of the 230 seats in thePortuguese parliament.
In November 2023, António Costa resigned as prime minister and party leader following theOperation Influencer investigation, which investigates suspected corruption activities in the awarding of contracts for the lithium and hydrogen businesses.[30] Following Costa's decision, anearly election was called for 10 March 2024.[31] Aleadership election was called for 15 and 16 December 2023, which was won byPedro Nuno Santos with almost 61 percent of the votes.[32]
On the 10 March 2024 election, the Socialist Party was narrowly defeated by theDemocratic Alliance (AD), headed by the Social Democratic Party, losing 42 seats and gathering 28 percent of the votes.[33] Three months later, in the2024 European Parliament elections, the Socialist Party narrowly defeated the AD coalition, by a 32 to 31 percent margin. A new election was called forMay 2025, after a vote of confidence in the AD minority government was rejected, following the revelations of theSpinumviva case.[34] The party suffered one of its worst results ever in the election, gathering just less than 23 percent of the votes and 58 seats, falling to third place in terms of seats by being surpassed by thefar-rightChega party and losing the status ofleader of the opposition.[35] Pedro Nuno Santos resigned and aleadership election was opened. After being the only candidate to submit a candidacy,José Luís Carneiro became party leader in late June 2025.[36]
Following the results of the previous legislative elections, many anticipated severe losses and an unprecedent electoral erosion, exacerbated by the term-limit rule that forced 54 out of the 148 sitting Socialist mayors elected in 2021 to step down, creating openings in several municipalities.[38] Despite this pessimistic outlook, the Socialists won 127 municipalities, but were still surpassed by the PSD, being 5 short of the minimum needed to retain the presidency of ANMP. The results were mixed for the party, in one handAlexandra Leitão lost Lisbon by almost 8%, the candidates in the biggest cities were also defeated and the party lost strongholds likeAljezur,Baião,Cabeceiras de Basto,Condeixa-a-Nova,Guimarães,Lourinhã,Melgaço,Soure andTorres Vedras; on the other hand the PS made significant gains in the interior of the country, notably flippingViseu for the first time ever. In response to the results, José Luís Carneiro declared that “the Socialists are back,” signaling party optimism despite not winning the major urban centers.[39]
Historically, during its first years, the party has also hadfar-left factions. The most notable figures of this factions include themarxist Manuel Serra, who opposedMário Soares leadership from the left and won 44% of the votes against him,[43] leaving the party and creating thePeople's Socialist Front afterwards;[44] as well as the MPsCarmelinda Pereira andAntónio Aires Rodrigues, who were the most notable examples of a "trotskyist infiltration on the party", it is noted that this faction represented 25% of the delegates elected to the socialist national congress of 1976.[45]