Premier Kathleen Wynne has extended the Liberals' decade-long rule of Ontario, winning a stunning majority mandate for her ambitious agenda of transit-building and a provincial pension plan – the largest new social program in a generation.

Her leftist campaign – which focused heavily on attacking Tim Hudak's Progressive Conservatives' plan to slash 100,000 jobs from the public sector, while portraying her as a sunny, energetic intellectual – allowed her to overcome her party's baggage, particularly the billion-dollar cancellations of two gas-fired power plants during the previous election campaign.

As of early morning Friday, the Liberals were elected or leading in 59 seats – five more than required for a majority. The PCs were elected or leading in 27 and the NDP in 21.

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Mr. Hudak conceded less than two hours after the polls closed and told supporters he would not lead the PCs into the next election in four years' time.

Her strong victory comes at a pivotal time for Canada's largest province, whose economy is still uncertain five years after the recession and faces a massive deficit. Ms. Wynne has vowed to reconvene the legislature within 20 days to reintroduce her budget, which was rejected by the other parties last month, bringing about the snap vote.

The premier is counting on increased infrastructure spending – $29-billion for new subways and highways over 10 years – to stimulate the economy. But how she will balance the books, which are $12.5-billion in the red, is an open question, and may require painful austerity that she has not yet spelled out.

The election, which polls said was too close to call in the final days, was actually over quickly once the counting began after polls closed at 9 p.m. ET.

Ms. Wynne's Liberals utterly dominated Toronto and the surrounding suburbs, and appeared poised to make gains in both. The PCs looked set to lose seats on the back of Mr. Hudak's hard-right platform, while Andrea Horwath's New Democrats made modest gains.

The Grits jumped out to a lead almost as soon as the polls closed and never lost it through the night. Around 9.30 p.m. ET, as it became clear they would win, supporters began to filter into Ms. Wynne's victory party in a downtown Toronto hotel ballroom, where the Premier was expected to speak later in the evening. They burst into a sustained, minute-long cheer at 10 p.m. ET when it was obvious Ms. Wynne had won a majority.

"Thank you for voting to build Ontario up. And let me tell you, your government is ready to do exactly that," Ms. Wynne told the packed room. "And let me tell you, we are going to build Ontario up for everyone in the province."

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Ms. Wynne – the province's first female premier and the first openly gay first minister in Canada – spent much of her speech highlighting the big-tent themes that drove her campaign.

"This is a beautiful, inclusive place that we live in, and I want us every single day to treasure that. I want our kids to feel that as they grow up in our schools and understand what a gift it is to live in a place like this where anyone can be the premier," she said. "Ontarians do not hold prejudice in their hearts, Ontarians want to be an open and inclusive people – we have so proven that."

In the province's most starkly contrasting campaign in a generation, Mr. Hudak ran as far right as Ms. Wynne ran left. The Tories promised public-sector job cuts, to slash corporate taxes to the lowest level in North America and kill business subsidies.

Most of the Liberal campaign was designed to make the election a referendum on Mr. Hudak, with Ms. Wynne urging centrist and left-leaning voters to rally around her to stop him.

Mr. Hudak, who had gone into the campaign the perceived front-runner, came out the night's biggest loser.

In the quaint country hall in Grimsby, Ont. where the PC party hosted its election party, there were tears and shouts of disappointment as the Tory leader announced his resignation.

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"We ran a campaign of hope because I have boundless hope for Ontario," Mr Hudak said as the sombre group cheered him on. "I truly believe that our best days are yet to come."

"I am immensely and forever proud of the campaign we ran," he added. But he acknowledged: "We did not achieve the result we wanted."

Andrea Horwath's NDP, meanwhile, looked set to lose some seats to the Liberals but gain others from the PCs.

The party, which triggered the election last month by rejecting Ms. Wynne's budget, had high hopes of attracting Grit voters disaffected by the gas-plant cancellations, which were widely seen as political moves to save Liberal seats in the 2011 election.

But Ms. Horwath's campaign failed to catch fire. As she became increasingly desperate to peel away Liberals in recent days, she opted for an all-out assault on Ms. Wynne's party, branding it "corrupt." The strategy appeared to half-work, but also drove away much of Ms. Horwath's left-wing base, which criticized her for abandoning big-picture policy for small-ball, pocketbook populism.

Ms. Horwath promised supporters that New Democrat members of the legislature will "work day in and day out" to hold the government's feet to the fire.

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But she has gone from holding the balance of power in a minority legislature to being a third party with the Liberals holding a comfortable majority.

"The people of the province made their choice based on a number of different issues. And now that they've made that choice, my job is to respect that choice," Ms. Horwath said at a suburban convention centre in Hamilton.

Ms. Wynne, running her first campaign since taking over from Mr. McGuinty early last year, spent much of the election trying to take the focus off her party's scandals and redirect it into a choice between herself and Mr. Hudak.

She stumbled badly during the lone televised debate – when she faced an all-out assault from the other leaders on the gas-plant scandal.

The Liberals were also thought to be at a disadvantage in the ground game. The party switched over to a new voter identification database just months before the election, and had to buy off-the-shelf software to match the Tories' proprietary software.

But in the end, Ms. Wynne's party overcame these problems, inflicting damage on Mr. Hudak with a series of devastating attack ads taking aim at his 100,000 job cuts.

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She was also helped by a platform further left than Ms. Horwath's. On top of the pension and transportation spending, she also promised raises for personal support workers and more money for various social programs. These moves helped take New Democrat supporters, as evidenced by Liberal leads in the province's most leftist ridings in Toronto.

At dissolution, the Liberals held 48 seats, the PCs 37 and the NDP 21. There was one seat vacant.

With reports from Kaleigh Rogers in Grimsby, Ont., Susan Krashinsky in Hamilton, and Joe Friesen in Toronto