In 1965, the PSU aligned with the SFIO and the PCF in supporting the candidacy of François Mitterrand in the presidential election. In contrast with the established socialist parties, the PSU also supported the student riots of May 1968; it subsequently moved away from cooperation with the Socialist Party (PS) which succeeded to the SFIO after 1969, and developed its own program, based on autogestion (workers' self-management).
Michel Rocard was the PSU candidate for the 1969 presidential elections, obtaining 3.61% of the vote in the first round.
The party again campaigned for Mitterrand in the 1974 presidential elections — a move which encountered the opposition of the PSU's own supporters at grassroots level; the PSU did not sign Mitterrand's Common programme of the Left (agreed with the Communists), and a sizeable section of the party activists, led by Michel Rocard and Robert Chapuis, left to join the renewed Socialist Party (believing that they could better function as a leftist tendency with the PS). The PSU supported the self-managed Lip factory.
PSU introduced Huguette Bouchardeau as its candidate for the 1981 presidential elections; she obtained 1.1% of the vote in the first round. In the 1988 presidential elections, the PSU supported the communist dissident candidate Pierre Juquin, who obtained 2.1% of the votes in the first round. In 1989, PSU merged with the New Left for Socialism, Ecology and Self-management (Juquin's movement), and formed the Red and Green Alternatives (nowadays integrated in the group Les Alternatifs).