Supreme Court Voids Narrow Liberal Victory in Terrebonne, Triggering Federal Byelection

Canada’s highest court has overturned a razor-thin Liberal win in a Montreal-area riding, setting the stage for a high-stakes byelection and tightening the math for Prime Minister Mark Carney’s minority government.

In a swift decision delivered Friday, the Supreme Court of Canada nullified the one-vote victory of Liberal candidate Tatiana Auguste in the riding of Terrebonne, ruling that an error affecting a mail-in ballot compromised the integrity of the result. The judgment marks the first time since 1988 that a Canadian court has overturned a federal election outcome.

Auguste had narrowly defeated Bloc Québécois incumbent Nathalie Sinclair-Desgagné in last spring’s general election. However, the result came under scrutiny when it emerged that a Bloc supporter, Emmanuelle Bossé, was unable to cast her mail-in ballot due to an administrative mistake. Elections Canada acknowledged that an incorrect postal code printed on a return label caused Bossé’s ballot to be sent back to her own mailbox, effectively preventing it from being counted.

Sinclair-Desgagné challenged the result in Quebec Superior Court, arguing that the error had a direct impact on the outcome. The lower court dismissed her claim, but she appealed to the Supreme Court. After hearing oral arguments from lawyers representing both the Liberals and the Bloc Québécois, the Supreme Court overturned the earlier ruling within hours.

The court’s decision automatically vacates the Terrebonne seat and initiates the process for a federal byelection.

In a brief statement, Liberal Party spokesperson Matteo Rossi said the party respects the ruling. “We have taken note of the Supreme Court’s decision and remain confident in Canada’s democratic institutions,” Rossi said. “Tatiana Auguste ran a strong campaign, and we are ready to return to voters in Terrebonne whenever the byelection is called.”

On the Bloc side, there was visible relief. Sinclair-Desgagné, who first won the seat in 2021 by a margin of nearly 7,000 votes, reacted with a long exhale as the ruling was delivered from the bench. Bloc president Suzanne Proulx called for swift action. “Now that the seat is officially vacant, Terrebonne residents should be given the opportunity to vote again without delay,” she said.

Terrebonne has historically been unfriendly territory for the Liberals, who had not won the riding since 1980 before Auguste’s one-vote victory.

The Supreme Court’s ruling brings the number of vacant seats in the House of Commons to three, with two additional openings in Toronto. Prime Minister Mark Carney holds the authority to set the dates for all three byelections. While there is flexibility in the timeline, they are widely expected to take place before the end of summer.

A fourth vacancy could soon follow. Liberal MP Nate Erskine-Smith has indicated he intends to resign from his seat in Beaches–East York once Ontario Premier Doug Ford calls a provincial byelection in Scarborough Southwest. That provincial seat became open after New Democrat MPP Doly Begum crossed over to run federally as a Liberal candidate in Scarborough Southwest, a riding vacated by Bill Blair after he was appointed Canada’s High Commissioner to the United Kingdom.

Carney, who was in Tumbler Ridge, British Columbia, on Friday, did not comment publicly on the court’s decision.

Despite the political turbulence, the Liberals’ minority government is not immediately at risk. Even if the party were to lose all pending byelections, it would retain enough support in the House to survive confidence votes. However, each lost seat would further complicate any effort to inch closer to majority status through potential defections from opposition MPs.

For now, attention turns back to Terrebonne, where voters will once again determine who represents them in Ottawa this time under the watchful eye of a country reminded of the razor-thin margins that can shape its political future.