Most of the party's members are former followers of Bettino Craxi, who was convicted for corruption and whom New Socialists often portray as a victim of political persecution.

In 2007, several members also left to join the Socialist Party, allied with the centre-left, while what remained of the NPSI was merged into the centre-right PdL.

At its founding congress, the NPSI decided to enter the centre-right House of Freedoms (CdL) coalition led by Silvio Berlusconi (a former friend of Bettino Craxi) as the centre-left was considered too compromised with the Mani pulite investigation, upon which the old Italian Socialist Party was disbanded while the ex Communists were not touched.

The centre-right won the 2001 general election and Berlusconi appointed NPSI's Stefano Caldoro as Deputy Minister for Education in his government.

At the 2004 European Parliament election, the NPSI formed an alliance with small social democratic movements and parties such as Socialist Unity, founded and headed by Claudio Signorile.

The list, named United Socialists for Europe, gained 2.0% of the vote and two MEPs, De Michelis and Alessandro Battilocchio.

After winning the legal dispute for the symbol and the leadership of the NPSI, De Michelis led the party into an alliance with Gianfranco Rotondi's Christian Democracy for Autonomies (DCA) at the 2006 general election.

[17] After the split, both groups had a member in the Chamber of Deputies, namely Del Bue for the left-wing and Barani for the right-wing (led by Caldoro).

[19][20] Since that moment, the only NPSI was that led by Caldoro, who announced that its party was interested in joining The People of Freedom (PdL) along with Forza Italia and National Alliance.

In 2015, Barani stepped down from secretary after having joined the Liberal Popular Alliance, formed by FI dissidents who wanted to explicitly support Matteo Renzi's centre-left government.

[22][23] Following Barani's move, the party appointed Antonio Fasolino as coordinator, chose to cut its official ties with FI and launched the so-called "dual membership".

[35] In July 2023, the NPSI formed an agreement with the Union of the Centre and Green is Popular / Christian Democracy with Rotondi in the Regional Council of Campania.