The Socialist Party (French: Parti socialiste [paʁti sɔsjalist], PS) is a social democratic French-speaking political party in Belgium. As of the 2024 elections, it is the fourth largest party in the Belgian Chamber of Representatives and the second largest Francophone party. The party is led by Paul Magnette. The party supplies the Minister-president of the French Community (Rudy Demotte), and the Brussels-Capital Region (Rudi Vervoort). In the German-speaking community, the party is known as the Sozialistische Partei (SP).

The PS is very commonly part of governing coalitions, and dominates most local authorities because of the extremely fragmented nature of Belgian political institutions, particularly in Francophone areas. In the years since 1999, the PS has simultaneously controlled five regional executive bodies: the Government of the French Community, the Walloon Government, the Government of the Brussels-Capital Region, as well as the COCOF, a local subsidiary in Brussels of the French Community Government, and the Government of the German-speaking Community.

The party, or its members, have from time to time been brought into connection with criminal activities and political scandals, mostly concerning bribery and financial fraud (Cools assassination, Agusta scandal, Dassault Affair, Carolorégienne affair, ICDI affair). The Carolorégienne affair caused Jean-Claude Van Cauwenberghe to step down as Minister-President of the Walloon region.

The PS is a centre-left party. Its ideology and image are a mix of social democracy and modern electoral marketing. In its political program, the party identifies as progressive and eco-socialist.

During the 2019 election campaign, the RePresent research centre — composed of political scientists from five universities (UAntwerpen, KU Leuven, VUB, UCLouvain and ULB) — studied the electoral programmes of Belgium's thirteen main political parties. This study classified the parties on two "left-right" axes, from "-5" (extreme left) to "5" (extreme right): a "classic" socio-economic axis, which refers to state intervention in the economic process and the degree to which the state should ensure social equality, and a socio-cultural axis, which refers to a divide articulated around an identity-based opposition on themes such as immigration, Europe, crime, the environment, emancipation, etc.

The PS then presented the most left-wing programme, along with the PTB, on the socio-economic level (-4.43), and also left-wing on the socio-cultural level (-3.41).

The RePresent centre repeated the exercise during the 2024 election campaign for the twelve main parties. The PS's positioning shifted towards the centre, while remaining on the left, on the socio-economic axis (-3.57) and remained unchanged on the socio-cultural axis (-3.46).

The PS performed well in the 2003 general election but were overtaken as the largest Francophone party by the Reformist Movement in the 2007 general election.