After SDP and its coalition partners failed to achieve an agreement on forming a new government following the 2015 general election, the party returned to the opposition.

Like most parties created at the time, it was opposed to the communist government and wanted Croatia to secede from Yugoslavia, yet it had the distinction of being one of the few to present itself as left-wing.

In the first 1990 Croatian parliamentary election, SDSH joined the centrist Coalition of People's Accord and fared badly, winning only 21 out of 351 seats.

However, its position was strong enough to warrant ministerial posts in the national unity government of Franjo Gregurić which was in power from July 1991 to August 1992.

Before the 1992 parliamentary and presidential elections, SDSH was involved in bitter dispute with the SDP over its rebranding into the Social Democratic Party of Croatia.

Recent referendums In August 1998, SDP and HSLS leaders Ivica Račan and Dražen Budiša signed a coalition agreement and proceeded to run together in the January 2000 parliamentary elections.

In June 2001, the Istrian regionalist party Istrian Democratic Assembly (IDS) withdrew from the coalition government and its chairman Ivan Jakovčić resigned his post as Minister of European Integration, citing criticism of the way they governed Istria on the regional level which had been coming from other parties within the ruling coalition.

[19] The uneasy coalition broke apart in early July 2002 when Račan formally handed in his resignation following HSLS refusal to support the agreement made with Slovenia concerning the two countries' joint control of the Krško Nuclear Power Plant.

[21] The January 2000 election win and the defeat of the ruling HDZ was seen as a turning point as it marked the first transition of power in Croatia's young democracy and upon coming into power Račan's government was seen as the country's first staunchly pro-Western government following a decade of the "authoritarian and nationalist rule" of late President Franjo Tuđman.

[22] During its term, the country signed a pre-membership agreement with the European Union, which paved the way for the formal opening of membership negotiations in October 2006.

[22] Although the six-party coalition government made a clear break from the former regime, it nevertheless failed to handle the growing social problems, unemployment and economic difficulties.

Račan struggled to contain factional disputes within the coalition and appeared indecisive in dealing with Western demands to hand over war crimes suspects to the ICTY, as well as with extremists at home who vehemently opposed such extraditions.

In the 2005 presidential race, SDP opted to support independent incumbent Stjepan Mesić, who succeeded in winning his second term by an overwhelming majority of 65.9% of the vote in the run-off in front of HDZ candidate and runner-up Jadranka Kosor with 34.1%.

Five days after the election, amid speculations that SDP might assemble a governing coalition in spite of them failing to win outright majority, he was replaced in that role by Zoran Milanović.

They also manage to retain control of the economically most powerful parts of the country, including the capital Zagreb, the northern Adriatic city of Rijeka and also won in Istria (in coalition with IDS).

In the run up to the 2009–10 presidential race, SDP held a primary election for the very first time, in which party nominees Ljubo Jurčić and Ivo Josipović ran.

During 2012, a Law on medically assisted fertilization was enacted, health education was introduced in all elementary and high schools, and Milanović announced further expansion of rights for same-sex couples.

A new fiscalization law and the government's pursuit of dealing with the swiss francs crisis are regarded as some of SDP's biggest successes in power.

[43] The administration adopted a number of reforms in taxation in order to cope with the difficult economic situation amid the Great Recession.

[49] A bad economic situation weakened the originally strong public support for the Milanović government, which was demonstrated in the 2013 local elections.

[55] A vote of no confidence in Orešković in June 2016 resulted in an early parliamentary election in November which the SDP contested as the largest party in the People's Coalition.

The first round of the leadership election on 19 November 2016 failed to produce an outright winner, as none of the seven candidates gained the necessary majority of 50% + 1 of cast votes.

[56][57][58] In July 2021, intra-party clashes broke out between supporters of Grbin and Bernardić, followed by the expulsion of four MPs on charges of doing damage to party or refusing to actively participate in the May local elections.

Apart from the president and four vice-presidents (Biljana Borzan, Mirela Ahmetović, Ranko Ostojić, Mišel Jakšić), the main governing bodies of the party include the party presidency (Predsjedništvo, consisting of 18 elected members), the head committee (Glavni odbor) and the supervisory committee (Nadzorni odbor).

[66] SDP is also a full member of the Progressive Alliance of Socialists and Democrats (S&D) group in the European Parliament as of the accession of Croatia to the EU in 2013.