Mario Beaulieu

In April 2014, he declared his candidacy for the leadership of the Bloc Québécois and received the endorsement of the executive of the Bloc's youth wing,[6][7] former Parti Québécois legislative members Bernard Landry and Pierre Curzi, and the former president of the Mouvement Desjardins, Claude Béland.[8] Beaulieu, viewed as a "hardline" sovereigntist, promised to prioritize achieving Quebec independence above everything else.[9] On June 14, 2014, he defeated BQ Member of Parliament André Bellavance for the Bloc leadership with 53.5% of the vote.[10] Beaulieu took office as Bloc leader at the party's convention on June 25, 2014.

Shortly after his election, Beaulieu attracted controversy from within the party due to statements in his acceptance speech associated with the Front de libération du Québec and separate statements seemingly critical about the past leaders of the party, which drew criticism from former Bloc Québécois leader Gilles Duceppe and resulted in two party members announcing their intentions to leave the party.[11] In the weeks following his election, a number of riding executive members quit the party to protest Beaulieu's leadership and a number of individuals who had been considering running for the party in the next election removed themselves from consideration.[12] On August 12, 2014, the party's parliamentary caucus was reduced to 3 MPs after House Leader Jean-François Fortin quit the party to sit as an Independent MP. Fortin accused Beaulieu of "pushing a unidimensional, intransigent agenda that lacks rigour has put an end to the credibility established by (former leaders) Gilles Duceppe and followed up by Daniel Paillé, two leaders who merit great respect."[12] On August 25, 2014, André Bellavance, who had lost to Beaulieu in the leadership vote also resigned, reducing the Bloc to two MPs.[13] Bellavance told a press conference, in regards to Beaulieu: "His vision and orientation for the Bloc are diametrically opposed to mine. Mr. Beaulieu says he can unite the party; for me it’s not the case."[14]

With the party languishing as it was about to enter the 2015 federal election, Beaulieu entered into discussions with former party leader Gilles Duceppe in hopes of saving the Bloc from extinction. On June 10, 2015, Beaulieu and Duceppe jointly announced that Gilles Duceppe would be returning to lead the party into the election campaign while Beaulieu would relinquish the leadership but remain party president.[15] The party executive agreed on June 9, 2015, to split the positions of president and party leader in order to facilitate Duceppe's return. The changes were ratified by the party's general council on July 1.[16][17]

In the 2015 election, Beaulieu was elected in the riding of La Pointe-de-l'Île, the only Bloc MP elected on the island of Montreal. The party returned 10 MPs, but fell short of official party status.

Beaulieu was one of three Bloc MPs who initially supported Martine Ouellet's leadership during a caucus revolt and remained with the Bloc caucus when seven MPs resigned on February 28, 2018, to sit as Independents.[18] He later became critical of her leadership and campaigned for her removal for an upcoming leadership review, whilst staying in caucus. Beaulieu was named interim leader after Ouellet resigned over losing a party referendum on her leadership.

On August 22, 2018, he ceded the party presidency to Yves Perron as part of an agreement to reunite the party following the conflict over Martine Oulette's leadership. Beaulieu is to continue as interim leader, however, until a leadership election is held in 2019.[19][20] On January 17, 2019, he was succeeded as party leader by Yves-François Blanchet.[21]