When he first arrived at the Ontario legislature in 1990, few took much notice of the lanky lawyer swimming in an ill-fitting double-breasted suit, much less peg him as a future leader of the province.
Yet over the years, McGuinty managed to beat the odds again and again, from his unlikely rise to Liberal leader in 1996 to winning his third consecutive election last year — a feat unmatched by his party since Sir Oliver Mowat more than a century ago.
Along the way, he honed a political style that saw the Liberals through many of the obstacles they faced over the last nine years.
"Never too high, never too low" was the moderate motto McGuinty lived by, an extension of his straight-laced, father-knows-best image.
But the man dubbed "Premier Dad" decided to cash in his chips Monday, stepping down amid a series of scandals that seemed insurmountable, even for him.
He'd alienated a powerful ally — Ontario's teachers — by forcing a pay freeze to reduce the province's massive $14.4-billion deficit. Public sector unions declared war, vowing to withdraw their financial support and use their organizational might to defeat McGuinty in the next election.
They made good on their threat in a Sept. 6 byelection McGuinty orchestrated in an effort to win the one seat he needed to regain a majority government, putting boots on the ground in Kitchener-Waterloo to elect a New Democrat for the first time in the riding's history.
Adding to his troubles was a rare contempt motion over the costs of cancelling two gas plants in Liberal ridings and a criminal probe of the province's Ornge air ambulance service.
By tendering his resignation and shutting down the legislature, McGuinty bought time for his party to elect a new leader, mend its relationship with the unions and wipe the slate clean on the contempt motion.
But he bristled Monday at the suggestion that he was getting out while he could.
Throughout his political career, people have told him that it couldn't be done — that he couldn't win a seat as a Liberal, that he couldn't win the leadership, that he couldn't win the election, he said.
"In 2003, in 2007, in 2011, we went into each of those elections behind," McGuinty said.
"So of course there's still going to be a few people out there who are going to say, you can't win. It has nothing to do with that."
Growing up in Ottawa as the eldest son in a large Catholic family, McGuinty helped his busy parents care for his nine younger siblings. He worked odd jobs through high school to help out, from hospital orderly to a counsellor at his father's summer camp.
As premier, McGuinty would often draw from his childhood to impart a political lesson about the responsibilities of leadership. Sometimes it would take a humorous turn to his mother Elizabeth, a no-nonsense nurse, whose tough love kept his ego in check.
He studied science before turning to law. In 1980, he married his high-school sweetheart Terri, an elementary school teacher. Together, they had four children: Carleen, Dalton Jr., Liam and Connor.
McGuinty jumped into politics in 1990 under tragic circumstances. His father Dalton Sr., an English professor and provincial politician, died suddenly while shovelling snow and his eldest son was recruited to succeed him in Ottawa South.
McGuinty often joked that he was selected because the election signs already had his name on them.
He won the seat, bucking a New Democrat tide that washed the Liberals out of office.
Despite his bland public persona, McGuinty managed an upset victory in the 1996 Liberal leadership race after placing fourth in the first two ballots.
He spent the next seven years in Opposition, failing to lead the Liberals to victory in the 1999 election with the Tories branding him as not ready for prime time.
"I think he was an accidental party leader, he only got 17 per cent of the vote in the leadership convention that elected him, like Stephane Dion," said Nelson Wiseman, a politics professor at the University of Toronto.
"When I saw him in 1999, I thought, you know, looks like the Conservatives are right. This guy isn't ready to be premier."
But McGuinty rallied after some media grooming — by the same Chicago consulting firm that helped Barack Obama win the U.S. presidency — and rejigging of the party machinery.
In 2003, he beat the beleaguered Tories, who were dragged down by a series of scandals over the fatal shooting of an aboriginal protester, tainted water and a massive blackout.
His credibility took a hit shortly after he first became premier when he imposed a health-care premium of up to $900 per worker, despite signing a pledge during the campaign not to raise taxes. He insisted he had no choice because the Tories left a hidden $5.6 million deficit.
He did another flip-flop on taxes when Ontario was teetering on the brink of the global recession, combining the provincial sales tax with the federal goods and services tax after campaigning against the idea for years.
It showed that behind McGuinty's paternal image was a shrewd politician who was prepared to make unpopular decisions if he thought it was the right thing to do.
His political style is very similar to former Tory premier Bill Davis, who once described the secret to his success as "bland works," said Environment Minister Jim Bradley.
"I've never seen the man angry," said the 35-year veteran of the legislature.
"He may have been and held it back, but you don't see the open signs of anger that you see with others. He's very balanced."
McGuinty easily led the Liberals to a second straight majority in 2007 when then-PC leader John Tory made the unpopular promise of extending public funding to religious schools, effectively handing McGuinty the election victory.
McGuinty owes much of his electoral success to sheer dumb luck, said Wiseman. Ontario didn't elect him in 2003 as much as they threw out the Tories, who didn't provide much competition in the next two elections.
"Fortuna — as Machiavelli says — plays a large role in people's lives, and that applies to politicians no less than to others," he said.
Former finance minister Greg Sorbara — McGuinty's chief confidante, strategist and campaign manager — disagrees.
"It has to do with some really rock-solid sense of purpose and determination that's in his makeup," he said.
"When he sets out for a goal, he just works hard to get there."
During his time in office, the self-described "education premier" poured money into health care and schools, more than doubling government spending and the province's debt while racking up record deficits after the recession hit.
The Liberals faced other scandals involving grants to ethnic groups and a so-called "billion dollar boondoggle" at eHealth Ontario, both of which cost cabinet ministers their jobs. But McGuinty always bounced back.
It wasn't until this year's scandal at Ornge and the political decisions to cancel the gas plants that things started sticking to the "Teflon premier." With taxpayers on the hook for hundreds of millions of dollars for the plants, McGuinty seemed to recognize this time the public anger was being directed at him.
He plans to stay on as the MPP for Ottawa-South until the next election, but wouldn't comment on speculation that he may run for the leadership of the federal Liberals.
McGuinty will likely keep a tight lid on that decision, just as he did his resignation, which surprised his Liberal caucus.
Before leaving the room where he delivered his swan song, McGuinty offered a final piece of advice to his future successor.
"Don't screw it up."