Layton was 61 years old.
The New Democratic Party issued a statement Monday on behalf of Layton's wife Olivia Chow, and his children Sarah and Michael Layton.
"We deeply regret to inform you that The Honourable Jack Layton, leader of the New Democratic Party of Canada, passed away at 4:45 a.m. today, Monday, Aug. 22," the statement said.
"He passed away peacefully at his home surrounded by family and loved ones."
A funeral service for Layton is expected to be held Saturday in Toronto's Roy Thomson Hall.
In lieu of flowers, Layton's family is asking that donations be made to the Broadbent Institute, a think tank announced earlier this year for social democrat-leaning academics by former NDP leader Ed Broadbent.
In his final days, as it became clear that Canada's leader of the Official Opposition likely wouldn't survive his battle with cancer, he wrote a letter to be shared with Canadians after his death.
Various portions of the letter are addressed to Quebecers, to young Canadians, to members of his party, his caucus, and to party members and Canadians at large.
"My friends, love is better than anger. Hope is better than fear. Optimism is better than despair. So let us be loving, hopeful and optimistic. And we'll change the world," Layton said in concluding the positive, optimistic message.
Layton's death is not only heartbreaking in how quickly it came after he announced his illness on July 25, but that it came so soon after what is considered to be Layton's greatest political achievement.
After an entire life spent in politics -- first as an academic, then as a city councillor, then in federal politics -- Layton had been riding a wave of popularity ahead of his death. It was his personal popularity that many credit for the NDP's "orange crush" in the 2011 federal election. Buoyed by his party's success, Layton had even put the prime minister's office in his sights for the next election.
Now, with his death, those dreams come to an end and put the very future of his party into doubt.
While not everyone agreed with Layton's socialist views, there were few who didn't respect the man's passion and work ethic.
The politician who had once been a scrappy city councillor with a brash, sometimes strident style, matured into a federal party leader renowned for his dedication.
Layton's colleagues say he was a master politician who knew how to both work a crowd and work out compromise within his team. All the while, he seemed to never abandon the causes he held most dear: poverty, the environment, public transit, workers' rights.
In the 2011 election, voters who had once seemed a little wary of the camera-loving politician appeared to finally connect with Layton, embracing his energy, his no-nonsense approach and his promises to represent the average Canadian in Parliament.
Many voters, particularly in Quebec, said it was Layton himself that drew them to vote for his party and push the NDP into official Opposition status.
Layton had likely dreamed of reaching the higher echelons of power his whole life. He had been steeped in politics from an early age, growing up in Hudson, Que., under a father who was a cabinet minister in Brian Mulroney's government and who became the Progressive Conservatives' caucus chairman.
Layton's grandfather too was a cabinet minister, under Maurice Duplessis' Union Nationale government in Quebec, and his great-great-uncle was one of the Fathers of Confederation. The Layton political legacy continues today, with his son, Mike, now a Toronto city councillor as well.
Layton became student council leader in high school and was voted by classmates as most likely to become a politician. He went on to study political science at McGill University and received his PhD in Political Science from York University.
He briefly aligned himself with the Liberals while at McGill but, impressed by Tommy Douglas's opposition to the War Measures Act, he turned to the NDP in 1971.
Layton married at 19, wedding his high school sweetheart, Sally Halford. They had two children: Mike, the Toronto city councillor; and Sarah, who works for the Stephen Lewis Foundation.
But his marriage to Sally dissolved in 1983, shortly after Layton decided to leave behind life as a politics professor at Ryerson University (then called Ryerson Polytechnical Institute) and make a run for Toronto city council.
A few years later, Layton met Olivia Chow, who was then a school board trustee, and married her in 1988. She ran for Toronto city council in 1991, the same year that Layton decided to make a bid for mayor. Layton lost badly to June Rowlands; but Chow won her council seat.
Many have credited Chow, an ambitious politician in her own right, as being one of Layton's greatest assets, acting as both his closest adviser and his soulmate. Former Toronto city councillor Howard Moscoe told The Canadian Press he always thought of Layton and Chow as a single political-family unit.
"They were so good at playing the council," he said earlier this year. "They were kind of meant for each other."
Together, Layton and Chow became Toronto's political power couple, fighting for public transit, the homeless and sustainable urban development. As councillors, they were often accused of grandstanding, once wearing black gags to protest being silenced by other Toronto politicians when they attempted to object to a deal with Shell Oil.
Layton loved to spend time in the outdoors with Chow and cycled to work every day while in Toronto and worked out in the House of Commons gym every week while in Ottawa. NDP MP Pat Martin once said that Layton and Chow even thought of their work as recreation.
"I've never met anybody so perfectly matched to a life in politics," Martin said of Layton.
But Layton did have some brushes with controversy. In 1988, he came under fire when it emerged that he and Chow were living in a housing co-operative subsidized by the federal government, despite a combined income of $120,000. Toronto's solicitor cleared the couple of any wrong-doing, and the couple soon left the co-op and bought a house in Toronto's Chinatown.
In the 2011 election, three days before voting day, it emerged that Layton had also been caught up in a sting on a Toronto massage parlour. Layton insisted he had entered the salon seeking a legitimate shiatsu massage and didn't know the place was used for "illicit purposes." Police chose not to charge him in the sting.
Despite the scandals and Layton's failed 1991 mayoralty bid, his ambitions didn't falter; they simply shifted. In 1994, he decided to make a run for federal politics, vying for a seat in the riding of Rosedale. Again, he fared badly, finishing fourth.
He pressed on with his Toronto city council duties, but in another example of his trademark energy, he also took on work as well as the head of the Federation of Canadian Municipalities, where he said he broadened his understanding of the priorities of towns outside Toronto.
Along the way, Layton also penned three books; "Homelessness: the Making and Unmaking of a Crisis" in 2000; "Speaking Out: Ideas That Work for Canadians" in 2004 and "Speaking Out Louder" in 2006.
He ran again for MP in 1997, this time in the riding of Toronto-Danforth but lost yet again, to longtime incumbent Liberal, Dennis Mills. Layton was finally able to make his move into federal politics in 2003 by taking over as leader of the NDP from outgoing leader Alexa McDonough. He grabbed a seat in Parliament a year later, in the 2004 election.
In that first federal election campaign in 2004, Layton insisted to reporters without any irony that his aim was to increase the party's standings from 13 seats to 150. The party earned 19 seats. But the NDP was able to win 15 per cent of the popular vote -- its best result in 16 years.
Layton's flamboyant leadership style seemed to re-energize the party following the staid leaderships of McDonough and Audrey McLaughlin before her. He was constantly in front of the microphone, moving easily between English and French, always ready with the quick sound bites that had made him famous in Toronto.
But Layton stumbled in that first federal campaign when he accused then-Liberal prime minister Paul Martin of being responsible for the deaths of homeless people because he had failed to provide funding for affordable housing.
He managed to smooth out his edgy persona during the 2006 election campaign and consistently scored well in leadership polls, with voters giving him high marks in the areas of principle, honesty.
Queen's University political scientist Jonathan Rose told CTV.ca during the 2006 campaign that voters seemed to respond to Layton because of his tireless campaigning and infectious energy.
"He has all the hallmarks of what we demand from traditional leaders: a clear persona, someone who has a high trust level, and someone who is able to articulate clearly what they believe," Rose said.
Layton added 10 more seats for his party in the 2006 election, and then again in 2008, when the party's seat count rose to 37.
Throughout the 2008 election campaign, Layton opened every speech with the eyebrow-raising declaration that he was running to be prime minister. Longtime friend Peter Tabuns said at the time that Layton was never anything if not an optimist.
"He is one of the most optimistic and hopeful people that I know, and I think that gives him a lot of strength to get through tough times," he told CP.
Those tough times were soon to come, when Layton was diagnosed in early 2010 with prostate cancer. Layton chose to push through it, taking to the hustings for the 2011 election campaign with the save fervour as ever. He even suggested the illness gave him further motivation.
"People that go through serious illness – you can either go one way or the other. You can either become despondent about it all. Or it kind of rejuvenates you, makes you focus on what's important," he said in an interview with Metro news.
The election began as a traditional two-horse race between the Conservatives and the Liberals, but at some point after the leaders' debate, Layton surged. Layton was suddenly no longer the third-place outsider; he was being embraced as the candidate of hope and change for those opposed to the Conservatives.
Election Day brought what became known as the "orange crush": 31 per cent of the popular vote for the NDP, 59 seats in Quebec, as well as 44 other seats across the country -- the party's best showing ever.
Former Progressive Conservative prime minister Brian Mulroney told CTV News afterwards that he believed Quebecers embraced Layton because they thought of him as one of their own.
"He's always referred to here as, ‘Our boy, Jack, a good guy,'" Mulroney said.
Ahead of the 2011 campaign, many had said that with four elections already behind him, if the NDP didn't make big strides, this would likely be Layton's final federal election.
In fact, it was Layton's last campaign. But not for the reason that anyone would have ever predicted.
