TORONTO

Dalton McGuinty -- the most successful Ontario Liberal premier since Oliver Mowat -- is stepping down.

His resignation sets off an immediate leadership campaign with his cabinet likely to produce several leading candidates -- possibly London North Centre MPP Deb Matthews, Don Valley West MPP Kathleen Wynne, Windsor-Tecumseh MPP Dwight Duncan and London West MPP Chris Bentley.

McGuinty, who in 1990 won his father's Ottawa riding after Dalton Sr. died suddenly shovelling snow, leaves behind a legacy of back-to-back-to-back Liberal governments.

"But way more important than our electoral victories is what they've allowed us to do," McGuinty said. "It's always been about families out there, their hopes, their struggles, their aspirations, their dreams, and all the hard work they do every single day to build a bright future for their kids and their grandkids."

The normally calm McGuinty teared up as, with wife Terri by his side, he told his Liberal caucus Monday evening that he would no longer serve as their leader, although he will represent his riding of Ottawa South until the next provincial election.

When asked what advice he would give to his successor, McGuinty joked, "Don't screw it up."

The premier's winning electoral record immediately inspired rumours he would run for the leadership of the federal Liberal Party and challenge Justin Trudeau, but he repeatedly deflected the question saying he had "no plans" to do so.

McGuinty also prorogued the house, bringing the current legislative session to an end, arguing the minority legislature is at a stalemate, unable to deal with the issues of the day.

"We've reached an impasse on a very important matter of public policy," McGuinty said of the government's as yet unsuccessful efforts to freeze public sector wages.

But the decison means MPPs will not return to work until a new Liberal leader is chosen, possibly until next year, despite having been called back two weeks early and passed little in the way of legislation.

His departure comes as his government battled contempt motions over its handling of cancelled gas plants in Mississauga and Oakville, and as public sector workers including teachers pushed back hard against his wage restraint measures.

In fact, the premier has fought to keep his customary control on the agenda since voters returned him to office last Oct. 6 with a minority government.

McGuinty told his caucus that while he had sometimes asked hard things of them -- his energy minister is currently facing two contempt motions over the gas plants -- he had learned from his parents the importance of sacrifice in making the world a better place.

The "Education Premier" will be remembered for his dedication and investment in education, including smaller class sizes, lower drop-out rates and full-day kindergarten.

McGuinty pushed green energy initiatives, an often controversial plan that angered many in rural communities, arguing that the benefit of this program would be a reduction in coal use and cleaner air.

Under the father of four, the Liberals banned cellphone use and smoking with kids in cars, pit bulls, smoking in all public places and homophobic bullying, earning him the nickname Premier Dad.

Spending ramped up dramatically since he gained office in 2003 -- after the market crash of 2008 Ontario became a "have-not" and piled up billions in new debt -- but McGuinty made no apologies for what he said was a necessary investment in public services after years of cutting under the Tories that preceded him.

"I'm not saying that our government has been perfect throughout -- we've made mistakes, we've fixed them and we've learned from them," McGuinty said. "But I am saying when it comes to the big things, those things that families absolutely have to be able to count on -- their schools, their health care, their environment and the economy -- we've always gotten the big things right."

McGuinty, who came from behind to win the leadership of the party in 1996, defied all pundits who argued he didn't have the royal jelly to be premier.

After a disappointing election campaign in 1999, McGuinty won decisively in 2003, 2007 and somewhat less spectacularly in 2011 -- each one, he pointed out, a come-from-behind victory.