Cardinal Robert Prevost, a little known missionary from Chicago, was elected as a surprise choice to be the new leader of the Catholic Church, becoming the first US pope and taking the name Leo XIV.
Pope Leo appeared on the central balcony of St Peter's Basilica after white smoke had billowed from a chimney atop the Sistine Chapel, signifying the 133 cardinal electors had chosen a new leader for the 1.4 billion-member Catholic Church.
"Peace be with you all," he told the cheering crowd, speaking in fluent Italian. He also spoke in Spanish during his brief address but did not say anything in English.
He has given few media interviews and rarely speaks in public.
US President Donald Trump swiftly congratulated Pope Leo on becoming the first US pope.
"Congratulations to Cardinal Robert Francis Prevost, who was just named Pope. It is such an honor to realize that he is the first American Pope. What excitement, and what a Great Honor for our Country," Mr Trump said on his Truth Social network.
The appointment was also welcomed by the Peruvian president Dina Boluarte.
"His closeness to those most in need left an indelible mark on the hearts of Peru," her office said in a post on X.
Leo becomes the 267th pope after the death last month of Pope Francis, who was the first Latin American pope and had led the Church for 12 years and widely sought to open the staid institution up to the modern world.
Francis enacted a range of reforms and allowed debate on divisive issues such as women's ordination and better inclusion of LGBT Catholics.
Watch: White smoke billows from the chimney atop the Sistine Chapel
Pope Leo thanked Francis in his speech and repeated his predecessor's call for a Church that is engaged with the modern world and "is always looking for peace, charity and being close to people, especially those who are suffering".
He had not been seen as a frontrunner and there was a brief moment of silence when his name was announced to the packed St Peter's Square, before people started to clap and cheer.
Read more: Leo XIV - soft-spoken pope with history of missionary work
SNAP, a US-based advocacy group for victims of clerical sex abuse, expressed "grave concern" about the choice, renewing accusations that he failed to take action against suspected predatory priests in the past in Chicago and in Peru.
"You can end the abuse crisis - the only question is, will you?" it said in a statement addressed to the new pope.
In an interview with the Vatican News outlook in 2023, Cardinal Prevost said the Church must be transparent and honest in dealing with abuse allegations.
Ahead of the conclave, some cardinals called for continuity with Francis' vision of greater openness and reform, while others said they wanted to turn back the clock and embrace old traditions.
Unlike Francis, who spurned much of the trappings of the papacy from the day he was elected in 2013, Pope Leo wore a traditional red papal garment over his white cassock.
The last pope to take the name Leo led the Church from 1878-1903. Leo XIII was known for his devoted focus to social justice issues, and is often credited with laying the foundation for modern Catholic social teaching.
Italian Prime Minister Giorgia Meloni was among world leaders to offer her congratulations.
"Italians will look to you as a guide and point of reference," she said. There has not been an Italian pope since 1978 and Pietro Parolin, the Vatican's secretary of state, missed out despite being on every media shortlist of contenders.
Pope Leo has attracted interest from his peers because of his quiet style and support for Francis, especially his commitment to social justice issues.
He served as a bishop in Chiclayo, in northwestern Peru, from 2015 to 2023.
Francis brought him to Rome that year to head the Vatican office in charge of choosing which priests should serve as Catholic bishops across the globe, meaning he has had a hand in selecting many of the world's bishops.
