Led by Robert Fabre during the 1970s, the party was the third partner of the Union of the Left. Nevertheless, its electoral influence did not compare with those of its two allies, which competed for the leadership over the left. Robert Fabre sought to attract left-wingGaullists to the party and gradually became close to President Valéry Giscard d'Estaing, who nominated him as Mediator of the Republic in 1978. He and his followers were excluded from the party by those who strongly supported the alliance with the PS.
Michel Crépeau was nominated by the party for the 1981 presidential election and obtained a disappointing 2.09% in the first round. He and his party in the runoff endorsed PS candidate François Mitterrand, who eventually won. The MRG won 14 seats in the subsequent 1981 legislative election and participated in PS-led governments between 1981 and 1986 and again between 1988 and 1993.
In the 1984 European elections, the MRG formed a common list with Brice Lalonde's environmentalists and Olivier Stirn, a centre-right deputy. The list styled as the Radical and Ecologist Agreement won 3.32%, but no seats.[12] The party resumed its customary alliance with the PS in the 1986 legislative election and supported President Mitterrand's 1988 reelection bid by the first round.
At the beginning of the 1990s, under the leadership of the popular businessman Bernard Tapie the party benefited from an ephemeral upswing in its popularity while the governing SP was in disarray. The list led by Tapie won 12.03% and 13 seats[13] of the votes in the 1994 European Parliament election. However, Tapie retired from politics due to his legal problems and the party, renamed the Radical Socialist Party (French: Parti radical-socialiste, PRS), returned to its lowest ebb.
Although the PRG remained a close and loyal ally of the PS, it has also cooperated with the small Ecology Generation (GE) party since December 2011.[16][17]
The PRG remained rather weak on its own electorally, averaging around 2% of the vote (2002 presidential candidate Christiane Taubira won 2.32% of the vote); which explains why the party depended on its stronger ally, the PS for support and parliamentary representation. Almost all of the party's deputies and local officials were elected with no official PS opposition. It retained some support among middle class voters and in traditional Radical areas in the South West.
The major exception was in Corsica, where the party was historically the largest party on the non-nationalistFrench Left and remains so to its time of dissolution due to a tradition of political dynasties (such as the Giacobbi family) and the weak infrastructure of the PS on the island. Paul Giacobbi represented Haute-Corse in the National Assembly until he stood down at the 2017 elections (Émile Zuccarelli, an internal rival of Giacobbi and current mayor of Bastia, also represented the island in Paris until his 2007 defeat) and Senators Nicolas Alfonsi and François Vendasi represented the Corsican PRG in the Senate. Giacobbi is also President of the General Council of Haute-Corse.
In metropolitan France, the PRG was able to sustain a long-lasting Radical tradition dating back to the French Third Republic, most notably in the southwest or departments such as the Eure-et-Loir and Eure.
The party was represented overseas in French Guiana by Taubira's Walwari, one of the major parties of the local left.
^Including 5 elected on PS-MRG lists in various departments.
^Results of the Entente radicale écologiste pour les États-Unis d'Europe which included the MRG, but also ecologists (Brice Lalonde) and centrists (Olivier Stirn).
^Nicolas Hubé (2013). "France". In Nicolò Conti (ed.). Party Attitudes Towards the EU in the Member States: Parties for Europe, Parties Against Europe. Routledge. p. 24. ISBN978-1-317-93656-5.