Premier Kathleen Wynne says she will ask the lieutenant-governor to call a by-election in the riding of Whitby-Oshawa for Feb. 11.
The seat has been vacant since August, when Progressive Conservative Christine Elliott resigned months after losing the race for party leader to Patrick Brown.
The date of Feb. 11 is just days before the legislature resumes following its winter break.
All three parties have nominated their candidates in Whitby-Oshawa: Niki Lundquist, a labour lawyer, will carry the NDP banner, regional councillor Lorne Coe is the PC candidate, while regional councillor Elizabeth Roy is running for the Liberals.
Though the by-election has not yet been formally called, the Liberals have already been running radio ads featuring Wynne promoting their candidate.
In the 30-second radio spot, Wynne says one of the things she's most proud of is that Ontario no longer burns coal to generate electricity, and now has more wind and solar power on the grid.