An Elections Canada mistake that prevented a single ballot from being counted was serious enough to invalidate a federal election decided by one vote, the Supreme Court of Canada says.The court released its written reasons for its 6-3 decision overturning the 2025 election result in Terrebonne, Que., establishing that a serious administrative mistake can qualify as an “irregularity” under the Canada Elections Act even when there was no intentional wrongdoing.“This case is a powerful reminder that in a constitutional democracy every vote counts,” Justice Mahmud Jamal wrote for the majority.Blacklock's Reporter said Bloc Québécois candidate Nathalie Sinclair-Desgagné lost the April 28, 2025 election to Liberal Tatiana Auguste by a single vote following a judicial recount.The dispute centred on a mail-in ballot that Elections Canada never received.An Elections Canada employee mistakenly printed an incorrect postal code on prepaid return envelopes sent to several voters in Terrebonne. The employee discovered the mistake more than three weeks before election day but did not report it to supervisors or contact affected voters.One voter's completed ballot was returned to her by Canada Post after election day because of the incorrect postal code and was never counted.Sinclair-Desgagné challenged the result in Quebec Superior Court, arguing the Elections Canada mistake was an irregularity that affected the election result.The lower court rejected the challenge, finding the postal code error and failure to correct it were human mistakes without dishonest or malicious intent.The Supreme Court disagreed.Jamal said the relevant question was not whether election officials deliberately did something wrong but whether a serious administrative error interfered with a citizen's right to vote.“The key consideration is whether the administrative error was capable of undermining a voter’s franchise,” he wrote..The majority concluded the incorrect postal code, combined with Elections Canada's failure to correct the known mistake for more than three weeks, constituted a serious administrative error and therefore an irregularity under federal election law.Because the number of votes affected by the mistake was equal to the one-vote margin of victory, the court said there was doubt over who had actually won the riding.The court formally annulled the Terrebonne election in February after hearing Sinclair-Desgagné's appeal, with its detailed reasons.Chief Justice Richard Wagner and Justices Suzanne Côté, Malcolm Rowe, Nicholas Kasirer and Michelle O'Bonsawin joined Jamal in the majority. Justices Andromache Karakatsanis, Sheilah Martin and Mary Moreau dissented.Jamal cautioned the ruling should not encourage challenges over every mistake made during an election.Minor errors or problems quickly corrected by election officials would not meet the same standard if they had no effect on a person's right to vote, he said.The majority said overturning an election should remain an “extremely rare occurrence,” but concluded annulment was warranted when a known and correctable official mistake left uncertainty over the winner.The decision triggered a byelection in Terrebonne.Sinclair-Desgagné ran again but lost the April 13 byelection by 668 votes.“I think this is an issue that goes beyond party politics,” Sinclair-Desgagné previously told reporters.
