Supreme Court explains why it invalidated Liberal MP's 1-vote win in 2025 election

The Supreme Court of Canada heard an appeal of the election result in the federal riding of Terrebonne, near Montreal. (Justin Tang/The Canadian Press)Social SharingThe Supreme Court of Canada says it decided to invalidate a federal Liberal candidate's one-vote victory in the 2025 federal election to ensure public trust in the electoral process.

The court says the choice to annul the election result ensures that a federal election is not decided by a known and correctable administrative error.

Liberal Tatiana Auguste was declared the winner in the Montreal-area riding of Terrebonne by one vote over incumbent Bloc Québécois candidate Nathalie Sinclair-Desgagné in April 2025.

The Bloc candidate challenged the election results and demanded a byelection after a Bloc supporter complained that she had tried to vote by mail using a special ballot that was never counted.

A Superior Court judge rejected Sinclair-Desgagné's request for a new election, but the Supreme Court reversed that ruling in a split decision delivered from the bench in February.

Justice Mahmud Jamal wrote for the majority that an Elections Canada employee had known for weeks that some voters had been sent envelopes with incorrect postal codes, but the agency did not take steps to correct the error.

Auguste went on to win the riding for a second time in a byelection in April.