American Cardinal Robert Prevost elected new pope, will take the name Pope Leo XIV | Live updates

Cardinal Robert Francis Prevost has become the first-ever American elected as the leader of the Catholic Church -- now known by his pontifical name of Pope Leo XIV.

The 69-year-old, born on the Southside of Chicago, is seen as a diplomat of the church and was an important adviser to his predecessor, Pope Francis.

He became a front-runner to the papacy in the days before the conclave began, said the Rev. James Martin, a papal contributor to ABC News.

Leo emerged from the balcony of St. Peter's Basilica on Thursday evening to throngs of cheering crowds, following the signal of white smoke that emanated from the chimney atop the Sistine Chapel.

Leo is the fifth-most-popular name chosen by popes. Pope Leo XIV's full authority and jurisdiction begins immediately upon his acceptance of the office.

READ MORE | What we know about Leo XIV, the new American pope

Father James Martin, a papal contributor to ABC, said he knows Pope Leo, formally Cardinal Robert Prevost, describing him as "very-down-to-earth."

Martin told ABC News the new pontiff is a "very kind person, very reserved."

Martin previously said days before the conclave's start that the American cardinal was a front-runner for the papacy.

In his first words, Pope Leo XIV, history's first American pope Robert Prevost, said "Peace be with you."

Pope Leo XIV, formerly Cardinal Robert Prevost of the U.S., emerges from the Vatican balcony.

From the loggia of St. Peter's Basilica, he recalled that he was an Augustinian priest, but a Christian above all, and a bishop, "so we can all walk together."

He spoke in Italian and then switched to Spanish, recalling his many years spent as a missionary and then archbishop of Chiclayo, Peru.

President Donald Trump congratulated the new pope in a Truth Social post.

"It is such an honor to realize that he is the first American Pope. 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!" he said.