The congress was called by outgoing PSOE leader Alfredo Pérez Rubalcaba after his party's poor results at the 2014 European Parliament election, garnering just 23% of the vote.

The ruling Spanish Socialist Workers' Party (PSOE), amidst a climate of high unpopularity, was ousted from power with the worst election result since the first post-Francoist electoral process in 1977.

A series of negative regional election results throughout 2012, coupled with an internal crisis in 2013 and the threat of rupture from the party's Catalonia partner, the PSC, further weakened the PSOE, with Rubalcaba's leadership being put in question as his popularity ratings plummeted.

Polls show data gathered among PSOE voters/supporters as well as Spanish voters as a whole, but not among party members, who were the ones ultimately entitled to vote in the primary election.

Sánchez promised to be blunt with corruption cases within the party, to look forward the promotion of a federal amendment of the Spanish Constitution and that his Executive will report in an open assembly to the militants once per year.