In 2014, Pablo Iglesias appointed Errejón as campaign manager for Podemos in the  European Parliament elections of 2014.
The campaign was a success, and the new party won 1.2 million votes.

Errejón himself became one of the most prominent Podemos politicians in terms of public profile, featuring in TV shows like La Sexta noche.
On 15 November 2014, he was chosen as one of the 11 members of the Council of Coordination of Podemos, commissioned to the post of Secretary of Policy of the party executive board.

By late 2014 Errejón faced public scrutiny and criticism as he had allegedly breached the conditions of his contract as a researcher at the University of Málaga (UMA), as the latter demanded physical presence and reportedly Errejón did not attend the UMA.
Concerns on the incompatibility of his job as researcher with other paid activities (such as campaign manager) also appeared.
While his supervisor (fellow Podemos board member Alberto Montero) alleged Errejón had verbal permission to work long distance, an investigation by the UMA was opened, with the UMA announcing it would suspend Errejón's salary in December 2014.
However, eventually no disciplinary sanction was actually enforced by the UMA on Errejón, as Errejón had already asked that the contract not be renewed.

Errejón was the campaign manager for Podemos in the Andalusian parliamentary elections of 22 March 2015, in which the party won 15 seats.
In the same month, he participated as a speaker at the International Forum for Empowerment and Equality, held in Buenos Aires.
He was also campaign manager for the regional elections on 24 May that year.

Errejón ran as a candidate for Podemos in the December 2015 general election, and was included third in the party list for the Lower House in the constituency of Madrid.
Elected as a member of the Congress of Deputies, he joined the Committee on Finance and Public Administrations.
He also became the Spokesperson of the Podemos parliamentary group (effectively number 2 in the parliamentary group after Iglesias).
As no government could be formed during the 11th term of the Cortes Generales, a new general election for was called for June 2016.
Errejón ran third as candidate to the Congress in the Unidos Podemos list, a coalition between Podemos, United Left (IU) and other left-wing parties.
 
The 2016 election brought a breaking point in Podemos as both Iglesias and Errejón deemed the results of the election as a failure, but because of different strategical reasons; Errejón in particular resented the defence of Iglesias had made of the alliance with IU.
Errejón became the Spokesperson of the Unidos Podemos-En Comú Podem-En Marea Confederal Parliamentary Group.
During the 12th Congress of Deputies, he also joined the Constitutional Committee (in which he held the role of spokesperson of his parliamentary group) as well as the Committee on Finance and Public Function, the Committee on Finance and Public Administrations and the temporary Committee on the investigation of the alleged illegal funding of the People's Party.

From December 2016 to February 2017 the 2nd Podemos Citizen Assembly ("Vistalegre II") took place.
Errejón did not bid for the party leadership (with Iglesias standing as candidate for Secretary-General with the single alternative candidacy of Juan Moreno Yagüe) but presented a project (Recuperar la Ilusión) competing with another two alternatives (around Iglesias and Anticapitalistas, respectively) in the matter of the composition of the State Citizen Council and the voting of several party documents.
Iglesias confirmed his role as Secretary General and his platform commanded a qualified majority in the voting of the composition of the State Citizen Council, with Errejón's project obtaining roughly one third of the votes.
Iglesias thus imposed his vision and project in the party, in what it was considered then a triumph of the more left-wing faction of Podemos.
Just after Vistalegre II, Errejón was demoted from the position of Spokesperson of the Parliamentary Group in the Congress of Deputies and replaced b
In 2014, Pablo Iglesias appointed Errejón as campaign manager for Podemos in the  European Parliament elections of 2014. The campaign was a success, and the new party won 1.2 million votes.
Errejón himself became one of the most prominent Podemos politicians in terms of public profile, featuring in TV shows like La Sexta noche. On 15 November 2014, he was chosen as one of the 11 members of the Council of Coordination of Podemos, commissioned to the post of Secretary of Policy of the party executive board.
By late 2014 Errejón faced public scrutiny and criticism as he had allegedly breached the conditions of his contract as a researcher at the University of Málaga (UMA), as the latter demanded physical presence and reportedly Errejón did not attend the UMA. Concerns on the incompatibility of his job as researcher with other paid activities (such as campaign manager) also appeared. While his supervisor (fellow Podemos board member Alberto Montero) alleged Errejón had verbal permission to work long distance, an investigation by the UMA was opened, with the UMA announcing it would suspend Errejón's salary in December 2014. However, eventually no disciplinary sanction was actually enforced by the UMA on Errejón, as Errejón had already asked that the contract not be renewed.
Errejón was the campaign manager for Podemos in the Andalusian parliamentary elections of 22 March 2015, in which the party won 15 seats. In the same month, he participated as a speaker at the International Forum for Empowerment and Equality, held in Buenos Aires. He was also campaign manager for the regional elections on 24 May that year.
Errejón ran as a candidate for Podemos in the December 2015 general election, and was included third in the party list for the Lower House in the constituency of Madrid. Elected as a member of the Congress of Deputies, he joined the Committee on Finance and Public Administrations. He also became the Spokesperson of the Podemos parliamentary group (effectively number 2 in the parliamentary group after Iglesias). As no government could be formed during the 11th term of the Cortes Generales, a new general election for was called for June 2016. Errejón ran third as candidate to the Congress in the Unidos Podemos list, a coalition between Podemos, United Left (IU) and other left-wing parties.  
The 2016 election brought a breaking point in Podemos as both Iglesias and Errejón deemed the results of the election as a failure, but because of different strategical reasons; Errejón in particular resented the defence of Iglesias had made of the alliance with IU. Errejón became the Spokesperson of the Unidos Podemos-En Comú Podem-En Marea Confederal Parliamentary Group. During the 12th Congress of Deputies, he also joined the Constitutional Committee (in which he held the role of spokesperson of his parliamentary group) as well as the Committee on Finance and Public Function, the Committee on Finance and Public Administrations and the temporary Committee on the investigation of the alleged illegal funding of the People's Party.
From December 2016 to February 2017 the 2nd Podemos Citizen Assembly ("Vistalegre II") took place. Errejón did not bid for the party leadership (with Iglesias standing as candidate for Secretary-General with the single alternative candidacy of Juan Moreno Yagüe) but presented a project (Recuperar la Ilusión) competing with another two alternatives (around Iglesias and Anticapitalistas, respectively) in the matter of the composition of the State Citizen Council and the voting of several party documents. Iglesias confirmed his role as Secretary General and his platform commanded a qualified majority in the voting of the composition of the State Citizen Council, with Errejón's project obtaining roughly one third of the votes. Iglesias thus imposed his vision and project in the party, in what it was considered then a triumph of the more left-wing faction of Podemos. Just after Vistalegre II, Errejón was demoted from the position of Spokesperson of the Parliamentary Group in the Congress of Deputies and replaced b
Íñigo Errejón