The CUP's decision to vote against Mas led to his withdrawal and to the election of Carles Puigdemont, until then mayor of Girona, as leader of a CDC–ERC coalition government.

[11] The biggest election loser was Rajoy's People's Party (PP), whose electoral collapse—reduced to 4.2% of the share and 4 out of 135 seats—meant it would be unable to form a parliamentary group of its own in the Catalan parliament for the first time in history.

[d] Voting for the Parliament was on the basis of universal suffrage, which comprised all nationals over 18 years of age, registered in Catalonia and in full enjoyment of their political rights.

[16] The 135 members of the Parliament of Catalonia were elected using the D'Hondt method and a closed list proportional representation, with an electoral threshold of three percent of valid votes—which included blank ballots—being applied in each constituency.

[15] The president had the prerogative to dissolve the Parliament of Catalonia and call a snap election, provided that no motion of no confidence was in process and that dissolution did not occur before one year had elapsed since a previous one under this procedure.

[15] The 2015 election resulted in pro-Catalan independence Junts pel Sí (JxSí) (a coalition comprising the two main centre-right and centre-left Catalan parties at the time, Democratic Convergence of Catalonia (CDC) and Republican Left of Catalonia (ERC), together with several minor parties) and Popular Unity Candidacy (CUP) holding a slim majority of seats, despite not securing a majority of votes as was their objective.

President Artur Mas' JxSí coalition also fell short of its goal to secure an absolute majority on its own, obtaining 62 seats against the combined 63 of the remaining opposition parties.

The CUP had difficulty in supporting Mas, whom they viewed as personally tainted by several corruption scandals involving his CDC party.

In the end, a last-minute deal was struck between JxSí and the CUP to ensure a pro-independence government under CDC's Carles Puigdemont, narrowly avoiding a new election being called and leading Mas to retire from frontline politics.

[20] This move sparked outcry within pro-independence ranks, including members within Puigdemont's coalition, who had aimed for a unilateral declaration of independence in response to the triggering of Article 155.

[5] Once Article 155 was approved, Mariano Rajoy dismissed the entire Catalan government from office and declared the Parliament's dissolution, calling a regional election for 21 December 2017.

[45][46] PDeCAT members sought to contest the election into a unitary list formed by pro-independence parties for the right of self-determination and against the use of Article 155, calling for "amnesty of political prisoners".

[62] On 13 November, the PDeCAT announced that it would run under the Together for Catalonia umbrella, centered around Puigdemont and including non-party members such as Jordi Sànchez.

[47][63] Republican Left of Catalonia (ERC) rejected the idea of renewing the Junts pel Sí alliance, and made its participation in any prospective electoral coalition conditional on it including the Popular Unity Candidacy (CUP) and members from Catalunya Sí que es Pot–in reference to the Podemos branch in Catalonia (Podem), led by Albano Dante Fachin, who had increasingly distanced himself from the party's national leadership.

[70] Podem's grassroots members voted in favour of an alliance with Catalunya en Comú, after Fachin had resigned as regional party leader over disputes with the national leadership.

The table below lists opinion polling on the perceived likelihood of victory for each party in the event of a regional election taking place.

[112] One of these was Junqueras, who sought to become president himself on the grounds that he could be granted prison permits that allowed him to attend parliamentary plenary sessions, whereas Puigdemont would have it near-impossible to be invested from Brussels—Parliament's regulations required for any candidate to the office to be physically present in the investiture—or to rule Catalonia from abroad.

[116] Facing arrest on possible charges of rebellion, sedition and misuse of public funds, the Catalan parliament delayed Puigdemont's investiture after Constitutional Court ruled that he could not assume the presidency from abroad.

The next day and less than 24 hours before he was due to attend the second ballot, the Supreme Court announced that thirteen senior Catalan leaders—including Turull—would be charged with rebellion over their roles in the 2017 unilateral referendum and subsequent declaration of independence.

In anticipation of this ruling and in order to avoid appearing in court, Marta Rovira—ERC's general secretary and deputy leader to jailed Oriol Junqueras—fled the country to Switzerland in "self-exile".