Jorge Mario Bergoglio, the archbishop of Buenos Aires, has been elected the 266th Roman Catholic Church’s new Pope.
The Argentine cardinal is the first Latin American to be Pope.
He will call himself Francis I.
An hour earlier, white smoke billowing from the Sistine Chapel chimney announced to the world that cardinals gathered inside had made their choice.
Jorge Mario Bergoglio replaces Benedict XVI, who resigned last month saying he was not strong enough to lead the Church.
The 115 cardinals have been in isolation since Tuesday afternoon, and held four inconclusive votes.
At least 77 of them, or two-thirds, would have had to vote for a single candidate for him to be elected Pope.
Before the conclave began, there was no clear frontrunner to replace Benedict.
Crowds with umbrellas massed in the square flying flags from around the world.
The Catholic News Agency said people were running through the streets of Rome, hoping to reach St Peter’s Square in time for the appearance of the new Pope.