In the high-stakes “minority math” of Ottawa, Prime Minister Mark Carney is currently three seats away from a functional majority. While floor-crossings have bolstered his ranks, the final hurdle for the Liberal government may rest entirely on a single, high-stakes by-election in the Quebec riding of Terrebonne.

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The Legal Spark: A Single Vote

The drama began on February 13, 2026, when the Supreme Court of Canada took the rare step of nullifying the 2025 election result in Terrebonne.

• The Original Result: Liberal Tatiana Auguste won by just one vote ($16,737$ to $16,736$) over the Bloc Québécois (BQ).
• The Ruling: The court found that “defective envelopes” provided by Elections Canada prevented at least one valid mail-in ballot from being counted.
• The Consequence: Auguste was forced to vacate her seat, dropping the Liberal count and triggering a by-election that must be called by August 15, 2026.

The Liberal Majority Roadmap

To reach the 172 seats required for a majority, Carney is playing a tactical game involving floor-crossers and vacant seats:

1. The Floor-Crossers: Most recently, Edmonton MP Matt Jeneroux left the Conservatives to join the Liberals, marking the third such defection since Carney took office.
2. The Toronto Strongholds: Two safe Liberal seats (University—Rosedale and Scarborough Southwest) are vacant following the departures of Chrystia Freeland and Bill Blair. These are widely expected to remain Liberal.
3. The Terrebonne “Hinge”: If the Liberals sweep the two Toronto by-elections and reclaim Terrebonne, they hit the magic number of 172.

The Majority Math at a Glance

Current Liberal Seats	Required for Majority	Gap
169 (including Jeneroux)	172	3 Seats

Why Terrebonne is Different

Unlike the “safe” Toronto ridings, Terrebonne is a battlefield.

• Historical Context: Except for a brief NDP “Orange Crush” period, the riding has been a Bloc Québécois stronghold since 1993.
• Current Odds: Analysts (including 338Canada) currently give the Liberals only a 34% chance of holding the seat against a resurgent Bloc.
• The “Trump Effect”: Carney’s path to victory relies on his personal popularity in Quebec—boosted by his “middle power” diplomacy against U.S. trade pressures—vying against the Bloc’s traditional nationalist appeal.

The Stakes

If Carney wins Terrebonne, he gains total legislative freedom. If he loses, he remains tethered to a fragile minority, likely forcing a general election later in 2026 to seek a direct mandate from voters.