Leo XIV's inauguration mass began in St Peter's Square on Sunday, attended by hundreds of dignitaries including US Vice President JD Vance and tens of thousands of faithful.
Chicago-born Robert Francis Prevost, who became the first US head of the world's 1.4 billion Catholics on 8 May, did his first tour of the square in his popemobile ahead of the mass.
Pope Leo XIVmade his debut tour of St Peter's Square, greeting tens of thousands of pilgrims and well-wishers ahead of his inauguration mass.
He stood in the white vehicle as it drove through cheering crowds, smiling, waving and making the sign of the cross.
US Vice President JD Vanceis among the hundreds of dignitaries due to attend the inauguration mass that begins at 10am local time (0800 GMT).
Leo will preside over the ceremony rich in rites and symbols, where he will receive his special papal ring before giving a homily that will set the tone for his papacy.
After spending two decades as a missionary in Peru, the 69-year-old is unknown to many Catholics, but during the past week he has offered glimpses of the kind of leader he will be.
In meetings with journalists, clergy and diplomats, he repeatedly called for peace in a world full of conflicts and defended social justice.
He also emphasised traditional Catholic values, including the importance of a family built around a "stable union of a man and a woman", and defended the rights of the unborn.
Inacia Lisboa, 71, originally from Cape Verde but who lives in Rome, said she got up early to get a good spot to see a man she said had already "entered my heart".
Asked what she wanted to hear from him, she told AFP: "The first thing is that he prays for us all, for peace in the world -- we need it so much."
Zelensky, Merz
Leo's elevation has sparked huge enthusiasm in the United States, which is being represented on Sunday by Vance, who converted to Catholicism in 2019, andSecretary of State Marco Rubio, also a Catholic.
Before becoming pope, the new pontiff on his personal X account reposted criticism of President Donald Trump's administration over its approach to migration