On Thursday, the 47-year-old Trudeau struggled to contain the uproar, begging forgiveness and confessing he failed to grasp how offensive his actions were.
"I have always acknowledged I came from a place of privilege, but I now need to acknowledge that comes with a massive blind spot," the son of the late Prime Minister Pierre Trudeau said to applause from a large crowd at a park in Winnipeg, Manitoba.
With Election Day just a month away, his chief opponent in the neck-and-neck race, Conservative leader Andrew Scheer, reacted by declaring Trudeau "not fit to govern this country."
Others wondered whether the incident would reinforce the belief among Trudeau's opponents that the boyish-looking sex-symbol politician is a lightweight, lacking in substance and maturity.
Trudeau, though, gave no sign whatsoever that he might resign, and there were no immediate calls from any leading figures in his Liberal Party to step down. Instead, many Liberals, some of them minorities, rallied around him, even as two more instances of him wearing brown- or blackface decades ago came to light.
"I think the real measure of the man, and I think the thing we need to be talking about, is all the amazing things we have done for diversity," said Greg Fergus, a Liberal member of Parliament who is black.
Fergus said there was a lot of confusion and hurt in the black community, but he noted that Trudeau apologized. And he pointed out that it was Trudeau who put Viola Desmond, a black woman who refused to leave the whites-only section of a Canadian movie theater in 1944, on the country's $10 bill.
Trudeau has long championed multiculturalism and immigration, with Canada accepting more refugees than the U.S. under the Trump administration. Half of Trudeau's Cabinet is made up of women, four are Sikhs, and his immigration minister is a Somali-born refugee. Canada has over 1.9 million people of South Asian descent out of a population of 37 million.
Defense Minister Harjit Sajjan, a Liberal who is Sikh, said that the brownface picture was wrong but that Trudeau has a record of standing up for minorities. Trudeau named Sajjan Canada's first Sikh defense chief in 2015.
Mitzie Hunter, a Liberal who is running to lead the party in Ontario and is black, tweeted: "I know it is not representative of the man he is. This is a teachable moment for all of us. I accept his apology and I hope Canadians do too."
Time magazine published the brownface photo on Wednesday, saying it was taken from the yearbook from the West Point Grey Academy, a private school in British Columbia where Trudeau worked as a teacher before going into politics.
It shows the then-29-year-old Trudeau at an "Arabian Nights" party in a turban and robe with dark makeup on his hands, face and neck. Trudeau said he was dressed as a character from "Aladdin."
"Darkening your face regardless of the context or the circumstances is always unacceptable because of the racist history of blackface," he said. "I should have understood that then, and I never should have done it."
West Point Grey Academy issued a statement saying the event was organized by a culturally diverse group of parent volunteers. "That said, we recognize that cultural sensitivities have evolved over the past 18 years," it said.
Trudeau said he also once darkened his face for a performance of Harry Belafonte's "Banana Boat Song (Day-O)" during a talent show when he was in high school.
And Canada's Global News TV network reported a third instance, broadcasting a brief video of Trudeau in blackface while raising his hands in the air and sticking out his tongue. A Liberal Party spokeswoman said the footage was from the early 1990s.
Scheer said his campaign team received the video from a concerned citizen and passed it on to the media.
Asked how many times he has worn brown- or blackface, Trudeau said: "I am wary of being definitive about this because the recent pictures that came out I had not remembered."
He said that he has dedicated himself as a politician to "counter intolerance and racism everywhere I can," and confessed to letting people down. "I stand here today to reflect on that and ask for forgiveness," he said.
Trudeau is the latest in a string of politicians to get in trouble over racially offensive photos and actions from their younger days. Earlier this year, Virginia Gov. Ralph Northam withstood intense pressure to resign after a racist picture surfaced from his 1984 medical school yearbook.
But Trudeau was already vulnerable over a political scandal that erupted earlier this year when his former attorney general said he pressured her to halt the prosecution of a Quebec company. Trudeau has said he was standing up for jobs, but the scandal led to resignations and a drop in his ratings.
Trudeau was also mocked at home and abroad for repeatedly dressing up in colorful, traditional Indian garb during a visit to India in 2018.
As for the brownface furor, "I am deeply troubled by what this means to Canada. Young kids are not just going to see just one or two but multiple images of the prime minister mocking their lived reality," said Leftist New Democrat leader Jagmeet Singh, who is a Sikh. "This is so hurtful to so many Canadians."
Political analysts were uncertain what effect it might have on the election, noting that race is not as combustible an issue in Canada as it is in the U.S.
Still, Robert Bothwell, a professor of Canadian history and international relations at the University of Toronto, said he was flabbergasted.
"That's the kind of thing you do when you are a frat boy," Bothwell said. "Maybe at 29 he had no idea that he was going to go on to greatness, but his father would have never done that."
He added: "The case has never been conclusively made that Justin is a person of substance. I mean, he may well be. But that impression is just not out there."