Pope Leo appeared on the central balcony of St Peter's Basilica about 70 minutes after white smoke 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," the Pope told the cheering crowd, speaking in fluent Italian.
He also spoke in Spanish during his brief address but did not say anything in English.
The choice of Prevost was announced by French Cardinal Dominique Mamberti with the Latin words "Habemus Papam" (We have a Pope) to tens of thousands of people gathered in St Peter's Square to hear the news.
Aged 69 and originally from Chicago, Prevost has spent most of his career as a missionary in Peru and became a cardinal only in 2023.
A member of the Augustinian religious order, Leo has given few media interviews and rarely speaks in public.
Leo becomes the 267th Catholic pontiff 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.
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".
Ahead of the conclave, some cardinals called for continuity with Francis' vision of greater openness and reform while others said they wanted to return to an embrace of old traditions.
Unlike Francis, who spurned much of the trappings of the papacy, Prevost wore a traditional red papal garment over his white cassock.
The last pope to take the name Leo led the Church from 1878-1903 and was known for his devoted focus to social justice issues, and is often credited with laying the foundation for modern Catholic social teaching.
Prevost has attracted interest from his peers because of his quiet style and support for Francis, especially his commitment to social justice issues.
Prevost 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.
Prevost said during a 2023 Vatican press conference: "Our work is to enlarge the tent and to let everyone know they are welcome inside the Church."
with DPA and AP
