Marit Stiles, the current education critic for Ontario's New Democrats, has become the first candidate to launch a bid to lead the party.
Stiles, a former school trustee, has been a legislator since 2018 and says she's focused on taking down the current Progressive Conservative government.
The party's top job became available after Andrea Horwath resigned on election night.
Horwath, who is now running for mayor in Hamilton, led the NDP since 2009 and saw it rise from third party to Official Opposition status in 2018 with 40 seats.
But the New Democrats slipped to 31 seats in this June's election.
The party has said a new leader will be in place by March 2023 and candidates have until December to register for the race.