Ontario by-election · September 3, 2026

A name, not a margin.

Mulroney is the most recognisable name of the three departures, which makes the measurement more interesting: her premium did not grow. It was 16.8 points in her first election and 16.4 in her last. A margin that arrives fully formed belongs to the riding.

Writ issued · polling day set

Live results

Connecting to the official count…

Preliminary results · Elections Ontario

The Vote-Scope forecast

Projected vote share (10th–90th percentile, median marked)

Susan Lahey Progressive Conservative

56.2 % Chance of winning: > 99 %

Naomi Davison Ontario Liberal

26.7 % Chance of winning: < 1 %

Bobby Nikmard Ontario NDP

8.5 % Chance of winning: < 1 %

Other

5.0 % Chance of winning: < 1 %

Matt Pearce Ontario Green

3.6 % Chance of winning: < 1 %

Three points are stripped from the Progressive Conservative baseline — a deliberately small correction, since the evidence points to a structural lean and no pre-incumbency period exists to prove otherwise. No by-election turnout residual is applied.

How this projection is built

Personal vote removed

3 points stripped from the Progressive Conservative baseline — the share that belonged to Caroline Mulroney rather than to the party.

58.8 % → 55.8 %

2025 result — the seat as it was won

Progressive Conservative 59.4 %

Ontario Liberal 23.9 %

Ontario NDP 7.7 %

Ontario Green 4.8 %

Other 4.2 %

40.3 %

Why this by-election exists

Caroline Mulroney is vacating the seat she has held since 2018.
Progressive Conservative share versus their province-wide score: +16.8 points (2018, her first election), +15.9 (2022), +16.4 (2025) — full from the start and flat thereafter.
Redistribution leaves no pre-incumbency observation for this seat, so the correction stays cautious rather than assuming the premium is entirely structural.
The Progressive Conservatives took 59.4% here in 2025 — the safest of the three Ontario contests. No candidates were named at the time of writing.

Sources