“I believe my past is my strength,” Mr. Martelly, 50, said in an interview, contending that voters know exactly what they are getting with him. “It’s open, public. It’s on YouTube.”

Supporters of his opponent, Mirlande Manigat, 70, a former first lady and college professor banking on her establishment credentials to sell stability, have used Mr. Martelly’s past to cast him as immoral and a risk. Some television stations that are supportive of her play the incriminating videos repeatedly.

Still, frustration with traditional politicians runs exceedingly high here, and Mr. Martelly’s supporters seem to be everywhere, wearing white and pink campaign shirts and scrawling on walls “Tèt Kale,” or “Bald Head,” a nickname for Mr. Martelly. Their passion, in fact, is what helped propel him into the final round of voting on Sunday.

After Mr. Martelly finished third in the first round in November — behind the top vote-getter, Ms. Manigat, and the handpicked candidate of the governing party — violent demonstrations helped push an international investigation of the election that ultimately led the government to drop its candidate from the runoff in favor of Mr. Martelly.

Now, Mr. Martelly draws the largest crowds and remains confident that the street buzz will lead him past Ms. Manigat.

Mr. Martelly’s other stumbling block may not be a candidate at all, but a former president, Jean-Bertrand Aristide, the popular former priest and two-time president he so obscenely dismissed. In another startling twist on the political scene here, Mr. Aristide left his exile in South Africa on Thursday evening and is expected to return to Haiti on Friday.

As for his angry tirade against the former president, captured in an undated but apparently recent video posted on YouTube, Mr. Martelly, whose politics tilt right, now says he was just venting his political differences with Mr. Aristide but is personally indifferent toward him.

“He has the right to come back to this country,” Mr. Martelly said. “The people behind me are the people behind Aristide. They are just looking for better days.”

If Ms. Manigat’s camp sees her as the mother who will soothe Haiti’s ills, Mr. Martelly comes across as the rebellious son who will shake things up.

He promises an anticorruption crusade, to eliminate what his campaign has identified as $900 million in “wasted money” in the Haitian government, and a back-to-the-land program to revive agriculture. Mr. Martelly, who was briefly in the Haitian Army in his youth, has also discussed restoring the feared military in a role akin to the National Guard in the United States.

He dismissed the most provocative notes of his Sweet Micky persona as a showbiz gimmick to sell records and provide the wherewithal for his family.

He said he spoke of his drug habit in a videotaped interview from 1993 to inspire people to break their own bad ways. He said he was never addicted and simply stopped using drugs after the birth of the first of his four children with his wife of 25 years, Sophia, whom he credits as a stabilizing force in his life.

Mrs. Martelly plays an active role in the campaign, saying she picked pink and white as the colors for his band — they signify love and peace — and, against the advice of consultants, insisted on them for his campaign.

“I said, ‘You guys have to swallow my pink,’ ” she said, as she reviewed campaign documents in the kitchen and prepared a dinner for Mr. Martelly.

Mrs. Martelly provided the early organizational muscle for the campaign before he brought in high-flying consultants who had worked on Senator John McCain’s 2008 presidential campaign and onFelipe Calderón’s successful candidacy for president of Mexico in 2006.

The consultants put Mr. Martelly through hours of study sessions, including lessons on how the government is structured. At some points, while admiring his gift for rallying a crowd, they sought to rein in his penchant for over-the-top antipolitician talk.

“I don’t even want to be president!” he exclaimed at early rallies.

“We told him maybe that is going too far,” said Damian Merlo, who worked on Mr. McCain’s campaign and is helping to manage Mr. Martelly’s.

Although Mr. Martelly used the nickname “president” as a performer and made biting, vulgar references to politics and politicians in song, he said he never harbored serious plans to run until after the January 2010 quake. Then a group of Haitian professionals persuaded him to enter the race last summer.

“And two months later I did not have a dime for the campaign,” he said, estimating that the first round ultimately cost him and his supporters $1 million and the second, backed by donors he refused to name, around $6 million.

Mr. Martelly said his financial house is in order, despite rumors of his being in heavy debt. The Miami Herald reported this month that lenders foreclosed on three of his properties in Florida three years ago, but Mr. Martelly described them as investments he did not personally manage and blamed the recession.

Mrs. Martelly acknowledged the country’s history of political leaders’ looting the treasury, but she said her husband could have returned to music if he needed money.

“We have taken a chance with politicians for the past 200 years,” she said. “What has that brought us?”