Cardinal Robert Prevost was elected as the new pope on Thursday, as white smoke rose from the Sistine Chapel on Thursday and the bells of St. Peter's rang out.
Prevost, who will go by Leo XIV, will succeed Pope Francis and take charge of the Roman Catholic Church.
"Peace be with all you," he said from the balcony of St. Peter's Basilica, in his first public words.
US President Donald Trump congratulated Pope Leo on his election to head the Catholic Church, and said it "is such an honor to realize that he is the first American Pope." Prevost is originally from Chicago.
"What excitement, and what a Great Honor for our Country. I look forward to meeting Pope Leo XIV. It will be a very meaningful moment!"
The election came on the first full day of voting by the 133 cardinal electors, who secluded themselves behind the Vatican's medieval walls on Wednesday afternoon.
A joyous crowd in St. Peter's Square cheered and applauded as the first puffs of smoke emerged from a small chimney on the roof of the Sistine Chapel, where the cardinals had been holding their secret ballot.
Prevost will then step forward to deliver his first public address and blessing to the gathered crowds.
Death of Pope Francis
Pope Francis died on April 21 after ruling the 1.4-billion member Church for 12 years. During his reign he sought to open up the staid institution to the modern world, enacting a range of reforms and allowing debate on divisive issues such as women's ordination and better inclusion of LGBT Catholics.
While no clear favorites had emerged to succeed him, Italian Cardinal Pietro Parolin, who served as the Vatican's number two under Francis, and Filipino Cardinal Luis Antonio Tagle were considered the frontrunners.
Other "papabili" - potential papal candidates in Italian - were France's Jean-Marc Aveline, Hungary's Peter Erdo, American Robert Prevost, Italy's Pierbattista Pizzaballa and Filipino Pablo Virgilio David.
The cardinals will have had to decide whether to pick someone to build on Francis' vision of greater openness and reform, or else choose a more conservative figure.
During the conclave their only communication with the outside world was through the smoke emerging from the chimney - black for no pope yet picked, white signaling a new pontiff chosen by a majority of at least two-thirds.
The cardinals held an initial inconclusive vote on Wednesday evening and a further two followed on Thursday morning. They returned to the Sistine Chapel at 4 p.m. (1400 GMT) and at around 6:08 p.m. (1608 GMT) the white smoke emerged.
During the conclave, cardinals were sequestered from the world and sworn to secrecy, their phones and computers confiscated, while they were shuttled between the Sistine Chapel for voting and two Vatican guesthouses to sleep and dine.
The average number of ballots it has taken to be elected over the past 10 conclaves was 7.2. Francis was elected after five in 2013.
This is a developing story.