Supreme Court of Canada annuls single-vote win in Terrebonne riding, vacating seat
The Supreme Court of Canada on Friday granted an appeal by a Bloc Québécois candidate who lost the federal election in Terrebonne riding
by a single vote
, vacating the seat and requiring a byelection to determine the winner.
Liberal Tatiana Auguste won the seat in the April 28 general election after a judicial recount, but Bloc Québécois candidate Nathalie Sinclair-Desgagné appealed to the courts, who found in Auguste’s favour. Auguste has been sitting as the MP for the riding since she was sworn in on May 22.
The federal government normally has six months to call a byelection when a seat is vacant.
On election night, the riding’s lead swung back and forth, and final preliminary results showed a narrow 25-vote win for Auguste. But when the tallies were validated, they showed a 44-vote lead for Sinclair-Desgagné, who was the incumbent MP.
A judicial recount followed, which flipped the result back to Auguste by a single vote.
The results were complicated after it was revealed an error by an Elections Canada employee put the wrong postal code on some special mail-in ballots, and one voter whose ballot was returned to her after election day revealed she had voted for the Bloc.
Quebec Superior Court Justice Éric Dufour ruled in October
the postal code error does not constitute an irregularity as defined under federal electoral law. “It is a simple human error, which sometimes occurs in general elections, committed inadvertently and without any dishonest or malicious intent,” the judge wrote.
Sinclair-Desgagné
appealed to the Supreme Court
, saying the Superior Court decision “contains several errors of fact as well as an interpretation of the law and jurisprudence that invites an appeal.”
The issue before the Supreme Court was whether this error constitutes an “irregularity” under the law. The court agreed with Sinclair-Desgagné’s legal team an irregularity does not require intentional or bad faith acts. And it rejected an argument from Auguste’s team the voter whose mail-in ballot was returned was “not prevented from voting.”
“Wait a minute,” Chief Justice Richard Wagner said in interrupting Auguste’s lawyer Marc-Étienne Vien during oral arguments Friday. “The aim of the law is to promote citizen participation at a time in history when institutions are under strain.”
Several other interruptions from judges followed.
“It seems to me the responsibility is totally clear,” Justice Malcolm Rowe said, adding responsibility for the error is on Elections Canada, not the elector.
The Supreme Court’s decision came after arguments Friday morning. A written decision in this case will come at a later date.
The vacancy reduces the Liberal Party’s seat count to 168, four short of a majority. Two other seats are vacant, University—Rosedale and Scarborough Southwest in Toronto, vacated by Christia Freeland and Bill Blair, respectively, since the beginning of 2026.
La Presse Canadienne contributed to this report.