The Socialist Party (Irish: Páirtí Sóisialach) is a political party in Ireland, active in both the Republic of Ireland and Northern Ireland.

The party has been involved in various populist campaigns including the Anti-Bin Tax Campaign and the Campaign Against Home and Water Taxes. Members of the party were jailed for their part in the former, while members have been arrested for their role in the latter. It had a seat in the European Parliament from 2009 to 2014. In 2015, the party received state funding of €132,000.

Internationally, it was affiliated to the Trotskyist International Socialist Alternative (previously the Committee for a Workers International) until 2024.^{[citation needed]} The Socialist Party is currently directly affiliated with ROSA – an "International Socialist Feminist Movement."

From 2014, the party's election candidates in the Republic did not stand for election directly on the Socialist Party platform, but have instead run as candidates as part of a faction of the Anti-Austerity Alliance (AAA), now Solidarity; which was a registered party in its own right between 2014 and 2015. Solidarity continues to contest elections as part of People Before Profit–Solidarity (PBP–S); a big tent coalition that includes People Before Profit. Socialist Party members Ruth Coppinger, Mick Barry and former member Paul Murphy, were elected in this way as TDs in the 32nd Dáil. Similarly, in 2016 the Socialist Party in Northern Ireland instead fielded candidates in the Cross-Community Labour Alternative. In 2022, however, the party ran once again in the North as the Socialist Party. As of 2024, Ruth Coppinger is the party's only elected TD.

The party was formed by former members of the Labour Party, collectively known as the Militant Tendency, who were expelled in 1989 having been accused of Trotskyist entryism.

The Irish Militant Tendency was aligned with Militant tendency in Britain, with both groups having been founding members of the Committee for a Workers International in 1974.

After its expulsion from Labour, they formed Militant Labour, which became the Socialist Party in 1996.

Militant Tendency in Ireland began in 1969 when Paul Jones, an Irish student who had joined Militant in Britain while he was a student in London, returned to Derry and began organising there, and also held meetings in Dublin. Peter Hadden, had similarly joined Militant when attending Sussex University in England and upon returning to Northern Ireland in 1971, began organising Militant there. The group grew on both sides of the border and practiced entrism in both the Northern Ireland Labour Party and the Labour Party in the Republic of Ireland. In 1977, they were expelled from the NILP and formed the Labour and Trade Union Group to contest elections in the north.