It was created in 1996[1] by a group that split from the United Left (IU) led by Cristina Almeida and Diego López Garrido.
PDNI was founded after the "Nueva Izquierda" (New Left, NI) internal current of IU that was critical with the leadership of Julio Anguita and his confrontational attitude with the Spanish Socialist Workers' Party (PSOE) were expelled from the governing bodies of the coalition.
This happened after the MPs linked with this current distanced themselves from the rest of the parliamentary group and refused to reject a labor reform that created a new type of contract, with a cheaper dismissal than the ordinary ones.
[2] The MPs of NI left IU and remained in Congress as part of the Mixed Group.
In 1999, PDNI sealed an electoral agreement with the Socialists to participate jointly in the next elections.