Former education minister Kathleen Wynne won the party's leadership race Saturday with 1,150 delegate votes, with longtime Liberal Sandra Pupatello finishing second with 866.
"This was the easy part," Wynne told the crowd of cheering delegates at the former Maple Leaf Gardens in Toronto after she was declared winner.
"Now we have the challenges ahead of us and we're going to need all of us working together."
Wynne will also make history as Canada's first openly gay premier, a subject she confronted head-on in a dynamic speech that wowed delegates Saturday morning.
Ontario is ready for a gay woman as premier, Wynne told the crowd earlier in the day.
"The province has changed, our party has changed. I do not believe that the people of Ontario... hold that prejudice in their hearts," said Wynne, who is married to Jane Rownthwaite.
Wynne delegate Alex Wilkinson, 24, said it's a significant milestone for the province and the country, which will have its sixth female premier when Wynne is sworn in.
"We can do it. You can be from Toronto, you can be a woman, you can be gay. You can do that and be premier at the same time."
Wynne has vowed to recall the prorogued legislature by Feb. 19 and said she would immediately try to meet with the opposition party leaders in an effort to make the minority government work.
"We're going to need all the ideas that came out of this campaign, we're going to need to put them together," she told the crowd.
"We're going to need to weave together a platform because we're going to have to have it ready at any moment to go into a campaign. But we're also going to need all those ideas to continue to govern."
Pupatello, a Windsor native who served as economic development minister before leaving the government in 2011, appealed to the party faithful to come together in her concession speech.
"Tonight we made history: our final ballot had two women on the ballot," she said to deafening applause. "Two strong women on the ballot."
Prime Minister Stephen Harper congratulated Wynne on her win, and thanked Premier Dalton McGuinty — who embraced Wynne onstage — for his service as premier.
"I look forward to working with Ms. Wynne on addressing issues that matter to Ontarians, and in particular the creation of jobs and economic growth," he said in a statement.
There were early signs that Wynne had momentum in the race, nearly tying Pupatello after the first ballot with just two votes between them.
Pupatello got a major boost from Harinder Takhar — widely seen as a stalking horse for the former MPP — and widened her lead after the second ballot.
But Wynne cleaned up as Eric Hoskins, Charles Sousa and finally third-place finisher Gerard Kennedy threw their support behind her, pushing her to the top.
Sousa's support surprised some observers, who believed the former banker and immigration minister would head to Pupatello's more right-leaning camp.
Sources say Mississauga's 91-year-old mayor Hazel McCallion helped convince Sousa — who holds a seat in the city west of Toronto — to cross the floor to Wynne. But Sousa said it was really about getting the legislature back.
Some speculated that Pupatello's desire to call a byelection to get a seat before bringing back the legislature may have turned the tide in Wynne's favour.
But her no-nonsense, professorial style — almost identical to McGuinty's — may have also been a factor.
McGuinty's "never too high, never too low" mantra carried the Liberals through nine years of ups and downs, and Wynne may have tapped into a vein of Liberals who want to stick with the moderate, centrist style that's allowed them to ward off the Progressive Conservatives and New Democrats.
Wynne insists she's different from McGuinty and the right leader for the times.
But as she takes the reins of power, Wynne will also have to deal with the baggage McGuinty left behind.
He's alienated a powerful ally the Liberals had courted for years — Ontario's public school teachers — by forcing a pay freeze to reduce the province's $12-billion deficit. Public sector unions, who protested by the thousands outside the convention hall, have vowed to use their organizational might to defeat the Liberals in the next election.
McGuinty also left behind a trail of controversies, from the political decisions to cancel two gas plants in Liberal ridings — at a cost to taxpayers of at least $230 million — to a criminal probe of the province's Ornge air ambulance service.
Sam Hammond, head of the union representing public school elementary teachers, said he wants to meet with Wynne, who has "a fresh opportunity to work to resolve" the labour strife.
"The sooner we can meet with the premier, the sooner we can work together to try and bring peace and stability back to our schools," he said in a statement.