Those endorsements, from Mississauga South MPP Charles Sousa and former Toronto MP and MPP Gerard Kennedy, came after the second ballot and pushed Wynne past longtime Liberal Sandra Pupatello, who up to that point held a slight lead between the two clear frontrunners.
"That was a critical moment when [Sousa] moved across the floor to us," Wynne told CBC's Susana Mas. Sousa and Kennedy were critical, she said, and would determine the winner. When she saw Sousa, Wynne didn't know at first where he was going.
"But when he started to move to us we thought, 'OK, this is fantastic momentum. We really are on our way,'" she said.
Wynne's victory on the third and final ballot came by a vote of 1,150 to 866 over Pupatello. The pair appeared together on stage and joined hands after the final results were announced.
Wynne said the province is ready to accept an openly gay woman as premier.
"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 Rounthwaite.
In a show of party unity, Wynne then asked all the candidates and all the Liberal caucus members to join her on stage.
"This is a dream team of candidates, this is a very deep bench," said Wynne after thanking all the candidates, her family and the campaign team.
She said with the "easy part" now over, her party must be ready for an election that could come as soon as this year.
"It's about taking the momentum and getting back to the legislature, getting to work and showing the people of Ontario that we can govern in a minority parliament," she said.
Five of the six candidates, including Wynne, represent Toronto, but Wynne said she would be "premier for the whole province."
Pupatello, Hudak, Harper offer congratulations
Pupatello congratulated Wynne and praised the Liberal team.
"Tonight we made history," said Pupatello. "Our final ballot had two strong women on the ballot.”
Wynne said Tim Hudak, Progressive Conservative leader, was the first politician to call and congratulate her.
"It was great, great of him to reach out," she said.
Prime Minister Stephen Harper issued a statement Saturday congratulating Wynne and saying he looks forward to working with her "on addressing issues that matter to Ontarians, and in particular the creation of jobs and economic growth."
Toronto Mayor Rob Ford also issued a congratulatory message to Wynne.
Wynne takes over a party with plenty of political baggage, including a $12-billion deficit and a soured relationship with the province's teachers, once a traditional base of Liberal support.
How Wynne won
Wynne, MPP for Don Valley West, finished second on the second ballot with 750 votes while Pupatello appeared to be in good position with 817.
Kennedy had 285 second-round votes to Sousa's 203.
Kennedy was expected to back Wynne but Sousa's endorsement came as a surprise.
In explaining his decision, Sousa told reporters he felt Wynne “has what it takes” to help the province return to fiscal balance while maintaining social programs.
"What's important is that we ensure that we renew our economy so we can afford social programs, health care, education and that we ensure that we balance our fiscal matters for the long term and I believe Kathleen has what it takes," Sousa said.
St. Paul’s MPP Eric Hoskins threw his support to Wynne after finishing last among the six candidates in the opening round. Harinder Takhar dropped out to back Pupatello shortly afterward.
Some speculated that Pupatello's lack of a seat in Queen's Park and her desire to call a byelection before bringing back the legislature may have turned the tide in Wynne's favour.
Jackie Blackett, speaking from Toronto’s gay village, said Wynne represents a refreshing change in Ontario politics.
"I think it’s great,” Blackett told CBC News. "It should be an equal opportunity for everyone. It just shows that society has really progressed. Personally I don't think anyone’s sexual orientation should be a factor."