Wynne, who resigned from cabinet on Friday, planted herself firmly as a centrist candidate, promising to play peacemaker over wage freezes with thousands of angry teachers while fighting a $14.4-billion deficit.
"We need to strongly articulate what our Liberal party stands for, and that is a progressive government (which) balances its responsibilities with its hopes," she told a packed room in her Toronto riding of Don Valley West.
"We have to know in our hearts and in our minds that the middle ground is the firmest place to stand."
The race was triggered three weeks ago when Premier Dalton McGuinty announced he would step down once a new leader was chosen, and prorogued the legislature.
He told all his ministers that they'd have to resign from cabinet if they wanted to run for his job.
Wynne, a former school board trustee, said what she can offer is experience and an ability to seek common ground on difficult issues.
"Because we can't move ahead in addressing our fiscal issues without good relationships with all of the workers of the province," she said. "It's just impossible. We need those relationships."
Four teachers protesting a controversial new anti-strike law outside Wynne's campaign launch said they hope she'll repeal it.
"I'm not sure, because she's come out several times and said that she felt she had to toe the party line, which is what I find really disturbing," said Paulette Dufort.
"I'm hoping that maybe she'll rethink that if she gets the Liberal leadership."
But when asked about the law, Wynne wouldn't say she'd repeal it.
"The legislation is in place, and there are conversations going on between teachers and boards right now," she told reporters after her speech. "What I know is that we need to rebuild those relationships, and if I'm lucky enough to be the leader of the party, then that is something that I will be focusing on is rebuilding those relationships."
The law, which passed with the help of the Progressive Conservatives, cuts benefits, freezes the wages of senior teachers and gives the government the power to stop strikes and lockouts.
Wynne was first elected in 2003 when the McGuinty Liberals took office. She served as education minister from 2006 until 2010, then transportation minister for nearly a year before moving to municipal affairs and aboriginal affairs after the 2011 election.
In 2007, Wynne beat former Progressive Conservative leader John Tory when he challenged her in the provincial election.
Wynne would make history if she won the leadership race, becoming Ontario's first female and openly gay premier.
Glen Murray, former minister of training, colleges and universities, pre-empted her announcement by launching his own bid on Sunday. Murray would also make history as Ontario's first openly gay premier if he wins.
He said he'll offer tax cuts for small businesses and rebates for middle-income families, along with "no money down" loans for university and college students.
But the former Winnipeg mayor, who was first elected to the legislature in 2010, offered little explanation of how he would do all he's promised while fighting the deficit.
While no members of the Liberal caucus showed up at Murray's launch, Wynne received three endorsements on Monday. Labour Minister Linda Jeffrey joined her on stage, along with Toronto MPP David Zimmer and former cabinet minister Monique Smith.
Ex-cabinet minister Sandra Pupatello and former MP Gerard Kennedy, who lost to McGuinty by just 140 votes in 1996, are also rumoured to be seriously considering leadership bids.
The list of potential challengers is dwindling rapidly. Finance Minister Dwight Duncan, Education Minister Laurel Broten, Economic Development Minister Brad Duguid and Energy Minister Chris Bentley — who won't seek re-election — have all crossed their names off.
The deadline to submit a bid is Nov. 23. McGuinty's successor will be elected by Liberals at a Toronto convention in late January.
But any candidate will have a heavy burden to bear in trying to rebuild the embattled minority Liberals, said the Progressive Conservatives.
The Liberals have been embroiled in a series of controversies over the costly cancellation of two gas plants, a criminal investigation into Ontario's Ornge air ambulance service and McGuinty's abrupt decision to shut down the legislature after announcing he'd step down.
Prorogation brought all legislative business to a standstill and killed planned committee hearings into the cancelled power plants in Oakville and Mississauga, as well as a rare contempt motion against Bentley.
"These people come from a cabinet that has taken Ontario to the brink," said Tory finance critic Peter Shurman, adding that 600,000 Ontarians are still out of work.
It really doesn't matter who succeeds McGuinty, said New Democrat Cheri DiNovo.
"Whoever is at the helm has to wear the decisions the Liberal party has made, particularly those who sat in positions of power at the cabinet table," she said.
"They're going to have to answer for the movement of the gas plants. They're going to have to answer for the sorry state of our economy and the lack of jobs."