Former Ontario cabinet minister Margarett Best will resign her seat in the legislature, triggering a fifth by-election in another test of support for Premier Kathleen Wynne's Liberals.
Ms. Best has been on medical leave since February, when Ms. Wynne demoted her from cabinet. She has since been absent from the legislature.
A Jamaican-born lawyer, Ms. Best was first elected in 2007 to represent Scarborough Guildwood, a largely blue-collar riding in suburban Toronto. She served first as minister of Health Promotion and Sport before she was shuffled to the Consumer Services portfolio after the 2011 election.
In a statement, Ms. Best listed her achievements, including banning smoking in cars with children, leading a successful bid for the Pan American Games and reforming the Condominium Act. She was also known for her concern about social issues.
"I want to thank all of my constituents for their support and friendship," she said. "It was an honour to serve each and every one of you as your member of provincial parliament and to represent such a diverse community. I take with me the satisfaction of being greatly enriched to have shared in your history, your culture, your ways of life and our common humanity."
Ms. Best did not return a phone call seeking comment Thursday afternoon.
Ms. Wynne praised Ms. Best as a "strong voice for Ontario's underrepresented communities."
"Since her election in 2007, Margarett has been a passionate advocate for social equality and has made a real difference in people's lives. She held several cabinet portfolios, served on many vital committees dedicated to poverty reduction and social health and introduced important legislative change," the Premier said in a statement.
The Liberals already face by-elections in Windsor, London, Ottawa and the Toronto suburb of Etobicoke.
Like the Etobicoke seat, Ms. Best's riding is in the Liberal heartland, the seat-rich suburbs ringing Toronto, where the party has built its support base. It is an area the Liberals must control to remain in power.
Ms. Best won her seat by comfortable margins. In the 2011 election, she was even able to grow her plurality despite a drop in support for the party provincewide.