2015 Barcelona City Council election
The 2015 Barcelona City Council election, also the 2015 Barcelona municipal election, was held on Sunday, 24 May 2015, to elect the 10th City Council of the municipality of Barcelona. All 41 seats in the City Council were up for election. The election was held simultaneously with regional elections in thirteen autonomous communities and local elections all throughout Spain.
The election was won by the Barcelona en Comú citizen platform, supported by Podemos, ICV–EUiA and Procés Constituent and led by popular activist and former PAH spokeswoman Ada Colau. Colau went on to become invested as the first female Mayor of Barcelona in history with the support of the Barcelona en Comú, ERC- and PSC-led coalitions and one of the CUP councillors. Incumbent Xavier Trias, who had campaigned for a second consecutive term in office, with his party Convergence and Union being reduced to 10 out of 41 seats in the City Council, from the 14 it had obtained in the previous election. Citizens became the third largest political force in the city, whereas Republican Left of Catalonia obtained its second best historical result.
On the other hand, both the Socialists' Party of Catalonia and the People's Party of Catalonia were severely mauled. The PSC, which had won every municipal election in Barcelona and had controlled the local government up until 2011, fell to 5th place and below 10% of the vote, while the PP achieved its worst result since AP result in the 1987 election. The Popular Unity Candidacy also entered the City Council for the first time in history, winning 3 seats and 7.4% of the share.
Electoral system
The City Council of Barcelona was the top-tier administrative and governing body of the municipality of Barcelona, composed of the mayor, the government council and the elected plenary assembly. Elections to the local councils in Spain were fixed for the fourth Sunday of May every four years.Voting for the local assembly was on the basis of universal suffrage, which comprised all nationals over eighteen, registered and residing in the municipality of Barcelona and in full enjoyment of their political rights, as well as resident non-national European citizens and those whose country of origin allowed Spanish nationals to vote in their own elections by virtue of a treaty. Local councillors were elected using the D'Hondt method and a closed list proportional representation, with a threshold of five percent of valid votes—which included blank ballots—being applied in each local council. Parties not reaching the threshold were not taken into consideration for seat distribution. Councillors were allocated to municipal councils based on the following scale:
| Population | Councillors |
| <100 | 3 |
| 101–250 | 5 |
| 251–1,000 | 7 |
| 1,001–2,000 | 9 |
| 2,001–5,000 | 11 |
| 5,001–10,000 | 13 |
| 10,001–20,000 | 17 |
| 20,001–50,000 | 21 |
| 50,001–100,000 | 25 |
| >100,001 | +1 per each 100,000 inhabitants or fraction +1 if total is an even number |
The mayor was indirectly elected by the plenary assembly. A legal clause required that mayoral candidates earned the vote of an absolute majority of councillors, or else the candidate of the most-voted party in the assembly was to be automatically appointed to the post. In the event of a tie, a toss-up would determine the appointee.
The electoral law allowed for parties and federations registered in the interior ministry, coalitions and groupings of electors to present lists of candidates. Parties and federations intending to form a coalition ahead of an election were required to inform the relevant Electoral Commission within ten days of the election call, whereas groupings of electors needed to secure the signature of a determined amount of the electors registered in the municipality for which they were seeking election, disallowing electors from signing for more than one list of candidates. For the case of Barcelona, as its population was over 1,000,001, at least 8,000 signatures were required.