Ontario Desk · By-elections
Three seats, three departures.
The writs were issued on August 5 for votes on September 3, and nominations close August 20. Two of the three seats are Progressive Conservative, and both are being defended without the member who won them — one of them amid the hotel controversy that cost him his cabinet post.
Called — September 3, 2026
The seat he built.
The Progressive Conservatives ran 11.7 points behind their provincial score here in 2018. Under Neil Lumsden — a former CFL player and Tiger-Cats executive — that deficit shrank to 0.9 points by 2025. He is gone, the party is carrying a scandal, and the Ontario Liberals now lead province-wide.
Favourite · Progressive Conservative 48 %
View forecast → Scarborough-Sud-OuestThe fortress predates her.
Doly Begum resigned in February 2026 to run federally — for the Liberals — and won in April. It is tempting to read the New Democrat share here as hers. The record says otherwise: the seat ran more than 22 points ahead of the provincial NDP before she was ever on the ballot.
Favourite · Ontario NDP 74 %
View forecast → York—SimcoeA 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.
Favourite · Progressive Conservative > 99 %
View forecast →No by-election turnout residual is applied to these races. The only one Vote-Scope has measured comes from the April 2026 federal by-elections; transposing it to a provincial contest would be an assumption rather than a measurement.