2026 Terrebonne federal by-election

A by-election was held on April 13, 2026, to elect a member of Parliament (MP) to represent Terrebonne, Quebec, in the House of Commons for the remainder of the 45th Parliament after the riding's result in the 2025 general election was annulled by the Supreme Court of Canada on February 13, 2026, vacating the seat held by the then-Liberal Party MP Tatiana Auguste. Auguste held the seat by a margin of less than a thousand votes.

The identity of the victor of the 2025 federal election in Terrebonne remained uncertain for close to a year following the election. Election night preliminary results had Liberal challenger Tatiana Auguste leading incumbent Bloc Québécois MP Nathalie Sinclair-Desgagné by thirty five votes. The lead was however short-lived as the tally verification process put Sinclair-Desgagné back in the lead by forty-four votes instead, a margin small enough to trigger an automatic judicial recount. The process also reported over 900 rejected ballots. The recount, overseen by Quebec Superior Court Justice Danielle Turcotte and conducted in early May, 2025 increased the total number of valid ballot by seventy-four. The lion's share of the gains went to Auguste, putting her back on top by a single vote margin, and she was declared elected accordingly. Auguste was subsequently sworn in and seated as MP for Terrebone.

A printing error on the special ballot return envelopes was reported after the recount was completed. Defeated MP Nathalie Sinclair-Desgagné contested Auguste's election at the Quebec Superior Court citing this printing error by Elections Canada as an irregularity, but her application was rejected in October 2025. She proceeded to appeal the ruling to the Supreme Court of Canada. Following a hearing by the full bench of Canada's top court on February 13, 2026, the election results was annulled and Auguste was unseated, leading to this by-election.

The top court's decision was the first time the election of a MP was successfully overturned through the contested elections provisions in the Canada Elections Act. The last time a seat was vacated by a court ruling was in 1989 when the Supreme Court of Ontario vacated the seat for York North under the previous Dominion Controverted Elections Act. The last time the nation's top court overruled a lower court's determination of a federal election outcome or voided a federal election outcome was over eight decades ago in 1942, when it unseated Liberal MP for Stanstead Robert Davidson for bribing voters with whisky and cash.

A writ for the by-election could be issued no sooner than February 27 and no later than August 1, 2026. Under the Canada Elections Act, the minimum length of a campaign is 36 days between dropping the writ and election day, but must not exceed 50 days. The by-election must also be held on a Monday within that time frame. Accordingly, the earliest possible date for the by-election was April 6 and the latest was September 28.

On March 8, the writ was issued for a by-election to be held on April 13. Nominations closed on March 23.

After reviewing its internal procedures, Elections Canada announced that, to avert the possibility of misdirected ballots in the future, special ballots will no longer be manually prepared by a riding office, but will be centrally and automatically prepared at its Ottawa office. However, the change was not expected to be fully implemented until the fall.

The candidates in 2025 have reappeared for the by-election:

• Auguste and Sinclair-Desgagné had already been confirmed as candidates before the by-election was called.

• Conservative Adrienne Charles's candidacy was announced on March 11. The Greens are fielding Benjamin Rankin again, as are the NDP with Maxime Beaudoin. Maria Cantore is also returning for the PPC.

The Longest Ballot Committee chose Terrebonne as their target out of three by-elections being held simultaneously. This resulted in a total of 48 candidates when nominations closed, and Elections Canada announced that write-in ballots similar to those used in Battle River—Crowfoot in 2025 would be employed.

Sinclair-Desgagné used the slogan Une voix qui compte! ("A voice/vote that counts!"). She promoted the Bloc platform for supporting seniors and first-time home buyers, and voiced concerns over the proposed routing of the Alto high-speed rail line and potential expropriations for it in the riding. Local observers noted that, besides the issue of the Alto line, other concerns included the construction of new housing and the decontamination of a former DND firing range to make way for a new interchange on Autoroute 640. Both the Bloc and Liberals agreed that the campaign is local. The Liberals concentrated their efforts on the ground, minimizing participation in local debates, but they still expected the result to be close.

Bloc leader Yves-François Blanchet laughed off suggestions that "fake candidates" could be nominated in the concurrent by-elections being held in Scarborough Southwest and University—Rosedale, in order to create extra campaign financing room in the Terrebonne contest.

At a Liberal rally, Auguste's advocate claimed that she had "won fair and square" in 2025, and that the Supreme Court of Canada (SCC) had later decided that it wanted to punish Elections Canada. At a subsequent Bloc rally, Sinclair-Desgagné described that as saugrenu ("absurd"), and said that people would find it strange that the Liberals would distance themselves from a decision of the SCC where normally it would be embraced by the party. That rally also featured posters bearing the slogan Reprenons notre place le 13 avril ("Let's take back our place/seat on April 13").

It was reported that the advance polls conducted a week before Election Day attracted a turnout of almost 20%, lower than the 25% seen in 2025, but almost double those happening in the Toronto-area by-elections.

2025 nullified result

2021 valid result (redistributed)

2021 valid result (actual)

• 2025 Terrebonne provincial by-election
• Terrebonne in the 2025 Canadian federal election