The 76-year-old Jesuit - the first non-European pope of the modern era - was introduced to the world from the balcony of St Peter's Basilica in front of tens of thousands gathered in the square below.
"Pray for me and I will see you soon," he told the rain-soaked crowd, asking them to pray for his predecessor Benedict XVI, who abdicated on Feb. 28. "Have a good evening and rest well."
Minutes earlier, white smoke rose above the Sistine Chapel and bells rang out across Rome, prompting cheers and wild applause.
NBC News Special Report: The Vatican announces that Cardinal Jorge Mario Bergoglio has been elected as the new head of the Catholic Church.
Seen as a compassionate conservative, the new pontiff is the son of a railway worker.
He prizes simplicity and humility and is expected to encourage priests to do shoe-leather evangelization, according to his biographer.
Bergoglio has only one lung, the other having been removed due to infection when he was a teenager.
He reportedly came in second during the 2005 balloting that ultimately elected Benedict XVI.
Smoke billowed from the chimney at 7:07 p.m. (2:07 p.m. ET) on the second day of behind-closed-doors voting and marked the beginning to a new era for a church combating scandal and internal strife.
The cardinals are thought to have taken five ballots to reach the two-third majority necessary for a decision.
Before being introduced from the balcony, the Argentine cardinal was taken from the Sistine Chapel into a side room called the "Room of Tears" to be dressed in the papal clothes.
His appearance was heralded by a Latin announcement beginning with the phrase "Habemus Papam!" meaning, "We have a pope!"
George Weigel, NBC News' Vatican analyst, said Pope Francis was the first Jesuit to become pontiff.
"He's a very brave man," he said. "He will be a great defender of religion around the world."
"The papacy has moved to the New World. The church has a new pope with a new name," he added. "I think it speaks to the church's commitment to the poor of the world and compassion in a world that often needs a lot of healing."
Edward Egan, the Archbishop Emeritus of New York, told NBC News' Brian Williams that this was "the moment of Latin America."
"I can assure you he's not feeble in any way at 76," he said.
'You're going to like him a lot'
Egan said Francis was "a man who calmly stands for what's right and just," and someone with "great compassion for the poor."
"I cannot tell you, Brian, how delighted I am," he said. "This is a man who I know and who was very, very good to me."
Egan said Francis was a "very good friend of mine," and he had "immense admiration for him."
"I think you're going to like him a lot," he added.
Now known as Pope Emeritus, Francis' predecessor Benedict watched Wednesday's events from a temporary lakeside residence at Castel Gandolfo while his permanent living quarters inside Vatican City are refurbished.
The behind-the-scenes ballot process that has taken place in the Sistine Chapel should still remain a secret. Both the cardinals and staff working alongside them swore an oath of secrecy as the conclave got under way, with the threat of ex-communication for anyone breaking the church's ancient code.
Such is the importance of secrecy that Vatican officials have installed jamming devices to prevent the use of cellphones by cardinals or hidden microphones by anyone wanting to hear their deliberations.
NBC News' Peter Jeary contributed to this report.