Tens of thousands of Catholics and political leaders, including U.S. Vice President JD Vance, will attend the inauguration mass of Pope Leo XIV on Sunday, marking the formal start of the first U.S. pope's papacy.

The ceremony will mark the formal beginning of the papacy of Robert Francis Prevost, who was chosen by fellow cardinals to lead the world’s 1.4 billion Catholics. The mass will take place at St. Peter’s Square, beginning at 10:00 a.m. (0800 GMT).

Prior to the service, Pope Leo XIV will make his first appearance in the popemobile at 9:00 a.m., a vehicle famously used by the late Pope Francis.

The mass will be a traditional ceremony, rich with rites and symbols. The new pope will receive his papal ring and give a homily that is expected to outline the priorities of his papacy.

At 69 years old, Leo XIV, originally from Chicago, is relatively unknown to many Catholics. However, in recent days he has offered glimpses into his leadership style. In meetings with journalists, clergy, and diplomats, he has repeatedly called for peace and social justice, reflecting a desire to address global conflicts. He has also shown a lighter side, meeting with men’s tennis world number one Jannik Sinner at the Vatican.

U.S. and global leaders attend

Leo’s papacy has sparked widespread enthusiasm in the U.S., with JD Vance, who converted to Catholicism in 2019, and U.S. Secretary of State Marco Rubio attending Sunday’s event.

Before becoming pope, Leo XIV had criticized the Trump administration’s immigration policies on his personal X account and had also criticized Vance, though those posts have since been deleted.

Vance was the last world leader to meet with Pope Francis before the Argentine pontiff’s death on April 21.

Among the notable dignitaries expected to attend are Ukraine's President Volodymyr Zelensky, German Chancellor Friedrich Merz, Argentine President Javier Milei, and European Commission President Ursula von der Leyen. Canadian Prime Minister Mark Carney, Israeli President Isaac Herzog, and several European royals will also be present.

Italian authorities have implemented extensive security measures for the event, deploying thousands of security officers, rooftop snipers, and anti-drone operations.

Tradition and ceremony

Pope Leo XIV, the 267th pope, was elected on May 8 following a conclave vote of cardinals that lasted less than 24 hours. He succeeds the charismatic but sometimes impulsive Pope Francis. His papacy comes at a time when the Church is still grappling with the legacy of the clerical child abuse scandal and attempting to adapt to the modern world.

Despite the Church's ongoing modernization efforts, Sunday’s inauguration will be steeped in tradition. No pope has been crowned during an inauguration mass since Pope Paul VI in 1963, but the event will remain a grand, symbolic occasion.

Leo XIV will first visit the tomb of Saint Peter, the first pope, located beneath the altar of St. Peter’s Basilica. He will then receive the pallium, a symbolic cloth worn over his chasuble, and the Fisherman’s Ring, which is uniquely crafted for each pope. The ring will be worn throughout his life and destroyed upon his death.

Following the ceremony, Leo XIV will greet delegations of heads of state, though it remains unclear whether any of them will have a private audience with the pope.