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

[2] All members of the Assembly of Madrid 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 regionally.

[18] Upon the publication of the dissolution decree the next day, the Assembly's bureau provisionally acknowledged the election call but announced it would study filling a complaint against it.

[43] Second deputy prime minister of the Spanish government Pablo Iglesias announced that he would be contesting the regional election as lead candidate for his coalition, Unidas Podemos.

[45] In March 2021, Toni Cantó, former leader of Citizens in the Valencian Community, announced that he would join Díaz Ayuso's candidacy,[46] which was accepted by the Electoral Commission.

[47] On 23 April, and following a death threat of unknown origin in the form of a menacing mail with four rifle bullets issued to Pablo Iglesias, Interior ministry Fernando Grande-Marlaska and Civil Guard director general María Gámez, a clash ensued between Iglesias and far-right Vox candidate Rocío Monasterio in the Cadena SER debate over the latter's refusal to explicitly condemn the incident.

Monasterio accused Iglesias of hypocrisy for refusing to condemn the assaults that Vox members had suffered on the campaign trail, while adding that "Spaniards just don't believe anything [the Spanish government] says" and casting doubts on the veracity of the threat.

This prompted Iglesias to walk out of the debate as he argued it risked "whitewashing fascism" and normalizing their arguments, which was followed by PSOE and Más Madrid candidates doing likewise shortly thereafter.

The tweet was deleted shortly after as a result of the media backlash it provoked, as it was seen as showing the party as supportive of Vox's stance not to condemn the death threat.

Vox intensified its aggressive campaigning style: after a controversial ad aimed at criminalizing migrant unaccompanied minors, which received criticism for its alleged "racism",[64] as well as Monasterio's performance in the debates being regarded as overtly disrespectful and undemocratic,[65] Vox leader Santiago Abascal overtly questioned the veracity of the death threats and accused Iglesias of being a "crybaby and coward" as well as "fucking spoiled child of Spanish politics".

Until then running a comfortable campaign propelled by favourable opinion polls, Vox's aggressivity placed Ayuso and her PP in a difficult position, as they were now required to distance themselves from the far-right party or face a possible backlash from the left-from-centre electorate.

The PP victory, which doubled its share of the popular vote from its worst historical result in the previous election, came at the expense of Citizens (Cs), whose support collapsed from 19.5% to 3.6%, below the five percent threshold, as well as the Spanish Socialist Workers' Party (PSOE), which scored in third place in the region for the first time in history.

[71] Podemos candidate Pablo Iglesias announced his retirement from politics after claiming to have been turned into "a scapegoat" who "mobilizes the worst of those who hate democracy".

[72] Más Madrid candidate Mónica García accepted her new role as leader of the opposition to Ayuso's government following her second-place performance amid the collapse of Ángel Gabilondo's PSOE.