Colau was able to retain the mayorship through an BComú—PSC alliance that received the support of Barcelona for Change (BCN Canvi) councillors under Manuel Valls, the former prime minister of France, who after his failed run at the 2017 French presidential election was nominated by the liberal Citizens (Cs) to become their mayoral candidate in his city of birth.

Valls's support of Colau's investiture was based on his stated intention to prevent the pro-Catalan independence camp from securing control over Catalonia's capital city.

Together for Catalonia (JxCat), the new brand of former Democratic Convergence of Catalonia (CDC) members who had openly embraced a Catalan independence ideology following the dissolution of the Convergence and Union (CiU) federation in June 2015, fell to fifth place to a record-low 10.5% of the vote under the leadership of Joaquim Forn, the former Interior minister who was at the time at preventive detention because of his involvement in the organization of the controversial 2017 Catalan independence referendum.

Concurrently, support for the People's Party (PP) plummeted even further to its worst historical showing, barely passing the five percent threshold with 5.01%, whereas the Popular Unity Candidacy (CUP) was expelled from the city council altogether.

[2] Below is a list of the main parties and electoral alliances which contested the election: According to a report from the Catalan newspaper Diari Ara, BCN Canvi–Cs candidate Manuel Valls would have received funds from a group of businessmen to prepare the campaign, that would have included a salary of €20,000 monthly for him.