Pope Leo XIV was elected as the Catholic Church's 267th leader on Thursday.
The temporary chimney atop the Sistine Chapel released a plume of white smoke on Thursday evening local time, signaling that the 133 cardinals working inside had reached a two-thirds majority to elect a new pope for the Catholic Church.
American Cardinal Robert Prevost was shortly thereafter announced as the 267th pontiff. He chose the name Leo XIV, a senior cardinal deacon announced.
The 69-year-old Chicago native is the first American pope and is seen as a diplomat in the church.
"This is the first greeting of the risen Christ. May the peace be with you," Leo said in Italian in his first remarks as pope. "This is the peace of the risen Christ."
Tune in to "The American Pope: Leo XIV," a special edition of "20/20," streaming now on Hulu and Disney+.
The Cardinals' Mass began in St Peter’s Basilica on Wednesday morning ahead of the papal conclave.
The mass, which was being broadcast live around St. Peter's Square was expected to last until 11:30 a.m. local time.
Later on Wednesday, the 133 voting cardinals will enter the Pauline Chapel at approximately 4:15 p.m. before a procession into the Sistine Chapel where they take the oath at around 4:30 p.m.
Of all the ceremonies associated with electing a new pope, the one most familiar to the general public is the smoke that emanates from a stovepipe chimney atop the Sistine Chapel after every round of balloting.
Black smoke -- fumata nera in Italian -- indicates an inconclusive vote, while white smoke -- fumata bianca -- will signify that a new pope has been elected. Along with the white smoke, the bells of St. Peter's Basilica will ring to proclaim the event to the world.
The ceremonial smoke is not created by the burning of the ballots. The voting slips are burned in a stove that dates back to the 1922 conclave and is set up for the occasion in the Sistine Chapel.
The smoke that wafts from the stovepipe chimney is created using chemical pellets that are burned in another stove that's connected to the chimney, which is temporarily erected atop the Sistine Chapel just for that purpose.
Assuming the elected cardinal accepts the office, the new pope's identity is typically revealed within an hour of the final ballot, after he chooses the name by which he will be known as pope.
The new pope then emerges onto the balcony to present himself to the world and deliver his first blessing to the crowd gathered below in St. Peter's Square.
-ABC News' Christopher Watson
As Vatican City begins to fill with the faithful on Wednesday morning, the weather forecast calls for temperatures in the mid-60 degrees Fahrenheit, with midday showers expected, according to the Italian Meteorological Service.
More than 25,000 people are expected to gather into St. Peter's Square on Wednesday, along with crowds of people spilling over into the nearby roads.
About 4,000 security personnel are on hand, along with about 1,000 volunteers. And about 5,300 journalists from around the world will be present, waiting for news from the conclave.
-ABC News' Joe Simonetti
Each member of the 133-cardinal conclave will write his choice on a paper ballot slip, fold it once in half and carry it held aloft between two fingers to the Sistine Chapel altar, where he will deposit it in a special urn placed there. In order to make the balloting secret, conclave members are instructed to write their votes "as far as possible in handwriting that cannot be identified as his."
Any conclave member who cannot attend in person due to illness or infirmity will cast their ballot from their room in the Domus Marthae Sanctae, where they're collected, placed in a lockbox and carried to the Sistine Chapel.
The votes are then counted by three scrutineers who affirm what is written on each ballot and then announce it to the conclave, so the cardinals can record the votes themselves. If the number of ballots cast is different than the number of cardinal electors, those ballots are discarded and burned and a new vote taken.
The candidate who secures two-thirds of the votes is elected pope.
Up to four rounds of voting can typically take place in a day. If no clear choice has emerged after three days, balloting is suspended for 24 hours to allow cardinal electors time to reflect. Another seven rounds of balloting then takes place, followed by another break, and so on.
If no pope is elected after 33 or 34 votes -- generally about 13 days -- then a new rule introduced by Pope Benedict XVI decrees that the two leading candidates as determined by previous ballots will engage in a runoff vote.
The candidates themselves, if they're members of the conclave, cannot vote in the runoff but are present for it. Whichever candidate receives the necessary two-thirds majority of the votes is the new pope.
-ABC News' Christopher Watson
