Broten _ a lawyer _ said she had advised Premier Kathleen Wynne that she will step down as the member for Etobicoke-Lakeshore effective July 2.
"After 10 years of practicing law, and nearly 10 years (in the legislature), it is time for me to look forward to the challenges of the next chapter in my career," she said in a statement.
"This was a very difficult decision for me to make, and one that was made after much soul searching and consultation with my family."
Broten was demoted from education to intergovernmental affairs after Wynne took over from Dalton McGuinty in February as part of the new premier's efforts to repair badly strained relations with the powerful teachers' unions, and was also given responsibility for women's issues.
"Laurel has been an integral member of our team, having served in such diverse portfolios as minister of children and youth services, minister of the environment and minister of education," Wynne said in a statement.
"In these roles, and in everything she did, Laurel was a tireless advocate for the women of Ontario."
Wynne announced she would take on intergovernmental affairs herself, and promoted Windsor rookie Teresa Piruzza to the women's issues portfolio.
Broten said she wasn't just leaving Ontario politics. She, her husband and twin sons are planning a move to Halifax before the school year starts in September.
"Whatever the future twists and turns my career will take, I am very hopeful that the next 20 years will be just as fulfilling as the last," she said.
"I want to especially thank Premier Wynne for giving me the privilege to serve...in this historic female-led government."
Wynne has six months to call a byelection in Broten's suburban Toronto riding, but she must call byelections in Windsor-Tecumseh and London-West by Aug. 15.
The premier also said she would call a byelection for Ottawa South to replace former premier Dalton McGuinty at the same time as she calls the Windsor and London votes to replace former cabinet ministers Dwight Duncan and Chris Bentley.
Wynne made no mention in her statement about when she would call the byelection to replace Broten.
The Liberals fell one-seat short of a majority government in 2011, so the outcomes of the four byelections would not change the balance of power in the minority parliament.