[4] Led by Holly Cairns since March 2023, the party was launched on 15 July 2015 by three independent TDs: Catherine Murphy, Róisín Shortall, and Stephen Donnelly.

Stephen Donnelly first entered politics as an independent TD in the 2011 general election, having previously worked as a consultant for McKinsey and Company.

[9][10] On 5 September 2016, Stephen Donnelly resigned as joint leader and left the party, stating that he was doing so "with great sadness, having vested so much together with my parliamentary colleagues, Catherine and Roisin, a small core team and many volunteers across the country, into the establishment of the Social Democrats over the last 20 months", but referring to his relationship with his fellow leaders, that "some partnerships simply don't work".

[16] In November 2019, the party contested 3 of the 4 by-elections caused by the election of Irish TDs to the European Parliament, but did not win any seats, with their candidates all receiving between 2.5% and 4.4% of the vote.

In the 2020 general election, the party ran 20 candidates in 20 constituencies, and increased their seats to six, despite a small fall in the number of first preference votes received.

[41] They performed particularly well in the Dublin City Council election, doubling their seat share to 10 and becoming the second largest party behind Fine Gael.

[42] In 2024, Dublin Bay South TD Eoin Hayes was suspended from the party after he confirmed he gave incorrect details about when he sold shares he held in a software firm Palantir that supplies technology to the Israeli Defence Forces.

[54] Sláintecare was developed as the result of a cross-Party Oireachtas Committee chaired by the Social Democrats' Róisín Shortall, which sought to examine the issue of healthcare in Ireland.

The party's Sláintecare policy plan also includes (but is not limited to): a legal entitlement to homecare packages for older people, significantly reducing prescription charges and lowering costs for medicines, providing access to basic procedures at a local level, and improved funding for mental health, including counselling, community programmes, and adult mental health teams.

[56][57] In May 2017, the party published the Urban Regeneration and Housing Bill to eliminate loopholes to the vacant site levy and increase penalties for developers engaged in land hoarding.

[60] In their 2020 manifesto, the party called for building 100,000 homes over a five-year period to be delivered by a new housing agency, and pledged to end homelessness.

[62][63] In their 2020 manifesto, the party said it would ban exploitative work contracts, encourage union membership and protect younger workers.

[64] The Social Democrats have published legislation on equal access and non-religious discrimination in schools,[65] extended unpaid parental leave[66] and greater minimum notice periods for residential tenancies.

[69] In their 2020 manifesto, the party committed to making primary school education free, reducing third level fees and expanding the SUSI grant system.

[72] The party has called for the establishment of an independent anti-corruption agency in Ireland to tackle white-collar crime and corruption in the corporate world and political spheres.

[77] As part of their 2024 manifesto, the party introduced a plan for a €10 million fund to bring Palestinian children to Ireland for medical treatment.