His high-profile position as head of the Vatican's office for bishops, his conservative leanings, his years in Latin America and his work in Rome as president of a key commission for Latin America all make him a favorite to become the first pontiff from the Americas.
By many accounts, Ouellet (pronounced Wehl-EHT') is not beloved in Quebec, where friends say he struggled following his appointment as archbishop in 2002. His comments condemning abortion even in the case of rape were attacked by politicians and commentators - sometimes viciously.
Some worry that the election of another conservative, intellectual pope known for his impenetrable speeches would further damage a church that is fighting losses in membership in Europe and North America due to growing secularism and sex abuse scandals. But the number of believers is growing in Africa, as well as Latin America.
Bookies give weight to Ouellet's accomplished resume when listing him among the top three likely future leaders of the world's 1.2 billion Catholics.
The 68-year-old Ouellet "knows a lot of people and a lot of people know him. And when I mean people, I mean those who count, the cardinals," said Anne Leahy, a former Canadian ambassador to the Holy See.
He is particularly well-regarded among cardinals from Latin America, a part of the world that is home to 40 percent of the world's Catholics. If the Latin American cardinals can't agree on one of their own, Ouellet's extensive experience there - he spent more than 11 years in Colombia - could work in his favor once the cardinals gather in the Sistine Chapel to elect a new pope.
Speculation that Ouellet could one day be pontiff started as early as 2003 when Pope John Paul II named him cardinal. His name came up after John Paul died in 2005, but he was considered a long shot because of his young age. Ouellet has since added to his resume.
Benedict XVI brought Ouellet to Rome to head the Vatican's office for bishops in 2010. It's an influential post that vets bishops' nominations worldwide. Ouellet also serves as president of the Pontifical Commission for Latin America, extending his influence over much of the Western Hemisphere.
"Cardinal Ouellet is a very powerful holy man," Cardinal Thomas Collins of Toronto told reporters in an interview. "He has been in South America. He's fluent in Spanish, he's fluent in Italian, French, English and German. And he's experienced in two different congregations in the Holy See. He's been a bishop. He's a scholar of the first rank. You put it all together and he's just a wonderful man, so you can see when people think of a pope they think of Cardinal Ouellet."
Born in the small town of La Motte, Quebec, Ouellet got his vocation to enter the church during a time of reflection after he broke his leg playing hockey. He was ordained in 1968 and taught in seminaries in Canada, Rome and Colombia.
His many accomplishments include a license in Philosophy from the St. Thomas Aquinas Pontifical University and a doctorate in dogmatic theology from the Pontifical Gregorian University, both in Rome.
Friends said his career stalled in 1994, when he went from being the rector of the prestigious Grand Seminaire de Montreal to the head of a seminary in Edmonton, Alberta.
Being a Quebecois who spoke poor English worked against him in Western Canada. But longtime friend Bishop Lionel Gendron, Ouellet's former superior who sent him there, said the experience was ultimately good for him because it improved his English.
After returning to Rome in 1996 Ouellet rapidly gained prominence and respect teaching at the Institute for Studies on Marriage and the Family at the Lateran Pontifical University.
He rose from teaching priest to cardinal in less than three years. Ouellet's doctoral thesis on dogmatic theology included a discussion on the thoughts of his friend Hans Urs von Balthasar, a Swiss 20th-century theologian who was highly regarded by Benedict.
"He's completely in the spirit of Benedict," said Michael Higgins, a Canadian who teaches at Sacred Heart University in Fairfield, Connecticut. "Whether that makes him the ideal pope for our time is a different matter."
Some in Quebec question whether another conservative intellectual cut from the same cloth as Benedict should be the next pope. And the papal buzz around him has received a mixed response in the increasingly secular province.
He made headlines in Canada with his comments condemning abortion even in cases involving rape. "There's already a victim. Should we be making another one?" he asked.
Reaction from politicians and commentators was swift and, in some cases, ferocious.
In one particularly strident reaction, a Montreal La Presse columnist, Patrick Lagace, compared Ouellet to the Iranian imam, Kazem Sedighi, who once suggested scantily clad women were to blame for natural disasters.
Legace said in an interview that he stands behind his comments today: "Cardinal Ouellet and Quebecers don't see eye-to-eye. He's part of this conservative strain of Catholicism that doesn't resonate in Quebec. When he speaks about Quebec, he's like someone out of space."
Ouellet also spoke out against gay marriage when Canada was in the process of legalizing it. Quebec, Canada's most liberal province, was very much in favor of it. Ouellet has also been criticized for remaining silent on the issue of sexual abuse by priests in Quebec.
Ouellet addressed the Catholic church's handling of its sex abuse scandals in an interview with the Canadian Broadcasting Corp that aired late Monday, saying he thinks the church's handling of it can be held up as a positive example.
"It is not a Catholic problem; it is a human problem," he said. "Most of the abuse occurred in families in very general in society, and my hope is what was done by the Catholic Church, which is not yet perfect, but could be also of example for others in society."
He said he was satisfied with the practices of monitoring members of the clergy which are currently in place.
Ouellet himself has addressed the speculation that he could one day be pope, telling an interviewer in 2011 that it would be "a nightmare" because it is a "crushing responsibility" and the "kind of the thing you don't campaign for."
But Ouellet seemed more open to it in his most recent interview, saying: "I have to be ready even if I think that probably others could do it better."
Louis Ouellet, Marc's older brother, said the cardinal returns home twice a year to see his family, including his 90-year-old mother, Graziella. Another brother, Paul, is a convicted sex offender and once took out an ad in a local newspaper in 2009 explaining why he pleaded guilty. Paul is not a priest.
Louis said the family is worried he won't be able to return home again if he does become pope.
"He's a family man when he is here and everybody likes to see him. There is a lot of love. He likes to eat with us, he likes to sing with us and enjoy being together with his family," he said. "If it happens, we are losing a brother, and my mother, she is losing a son."
Louis said Marc remains a hockey fan and is an avid swimmer.
"He will swim for three or four kilometers. Sometimes we're worried about him. He's out there all by himself and we lose sight of him," Louis Ouellet said. "But he always comes back."