The Supreme Court has now explained why a postal-code mistake by Elections Canada was serious enough to erase a federal election result, drawing a line between ordinary election-day errors and administrative failures capable of determining who sits in Parliament.
In written reasons released Friday, the Court said the issue in Terrebonne was not simply that an incorrect postal code appeared on a special-ballot return envelope. The error was known before election day, remained uncorrected, prevented an eligible voter’s ballot from being counted, and surfaced in a race ultimately decided by exactly one vote.
Justice Mahmud Jamal, writing for the majority, said annulling the result prevented a federal election from being decided by a “known and correctable administrative error,” according to The Canadian Press.
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The reasoning supplies the legal basis for a decision the Court had already made seven months earlier. On February 13, the Supreme Court overturned a Quebec Superior Court ruling and annulled the April 28, 2025 election in Terrebonne, but issued only an oral judgment at the time and said detailed reasons would follow.
The Supreme Court test in 2012
The ruling turns on Section 524 of the Canada Elections Act, which allows an election to be contested over “irregularities, fraud or corrupt or illegal practices” that affected its result.
The Supreme Court had already set a deliberately high threshold in its 2012 Opitz v. Wrzesnewskyj decision, saying ordinary administrative mistakes cannot routinely be used to overturn elections because doing so could itself undermine confidence in final results.
But the ruling also defined irregularities as serious administrative errors capable of undermining the electoral process and noted that the law could potentially cover a situation where an eligible voter was improperly prevented from voting because of an election official’s error. The Court said that question was not before it in 2012.
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Terrebonne presented almost exactly that scenario. Elections Canada said in May 2025 that some return envelopes for local special ballots carried an incorrect postal code for its Terrebonne office. Of 115 local mail-in special ballots issued, 85 arrived on time and were counted, five arrived late, and 16 were not returned to the office. At least one marked ballot was returned to the elector by Canada Post after election day.
Court filings cited in earlier reporting showed an Elections Canada employee discovered weeks before polling day that the wrong postal code had been placed on multiple envelopes but did not escalate or correct the problem.
The elector said she had voted for Bloc Québécois candidate Nathalie Sinclair-Desgagné.
The judicial recount produced 23,352 votes for Liberal Tatiana Auguste and 23,351 for Sinclair-Desgagné. The disputed ballot therefore equalled the entire margin separating the candidates.
Quebec Superior Court had concluded in October 2025 that the postal-code mistake was human error rather than an irregularity serious enough to undermine the integrity of the election.
The Supreme Court disagreed and annulled the result.
Elections Canada reviews ruling
Elections Canada responded Friday, saying it “will carefully review the Supreme Court of Canada’s decision made public today.” The agency said Chief Electoral Officer Stéphane Perrault will determine whether further action is required.
It said it had already completed a review of the special-ballot process following the 2025 election and implemented its recommendations. Those changes include peer and headquarters review of mail-return labels, stronger monitoring of ballot-return rates, upgrades to data systems, and automated printing of return-address labels intended to reduce manual errors.
In total, Elections Canada lists 13 recommendations from the review.
The February annulment triggered an April 13 by-election in Terrebonne. Auguste won again, this time with 22,445 votes against Sinclair-Desgagné’s 21,777, a margin of 668 votes.
While the practical dispute over who represents Terrebonne has therefore already been settled by voters, the Supreme Court’s reasons address the broader question left behind by the one-vote result: when a preventable administrative failure stops a valid ballot from reaching the count, Canadian courts can treat the mistake as serious enough to invalidate an election when the error places the winner itself in doubt.
