Pope Leo XIV, the first American pontiff of the Roman Catholic Church, will lead his inaugural mass on Sunday, according to the Vatican.

The mass, called the Holy Mass for the Beginning of the Pontificate, will begin in Vatican City on Sunday at 10 a.m. local time (4 a.m. ET), the Vatican Press Office said.

Before the start of the mass, Leo will wave to the tens of thousands of people expected to be in the crowds, according to officials.

The mass, which will be held in St. Peter’s Basilica, will begin by the tomb of St. Peter, according to Vatican officials.

During the mass, the Petrine Pallium and Fisherman’s Ring will also be presented to Leo, the press office said.

The Pallium — a narrow Y-shaped band woven in white and decorated with two black pendants, six black crosses and three pins representing Christ’s crucifixion — signifies the pontiff carrying on his shoulders the responsibility of shepherding the church.

The Fisherman’s Ring, a gold signet ring, symbolizes the new pope’s role as the successor of St. Peter, a fisherman who is considered to be the first leader of the church, according to the Vatican Press Office. The ring signifies the beginning and the end of a pope’s authority, with Francis’ ring ceremonially broken after his death. Catholics who meet the pope traditionally kiss the ring to demonstrate both their respect for the pontiff and their devotion to the church.

Leo will then deliver a homily, followed by a prayer, called the Regina Caeli, according to the Vatican. The event is expected to be approximately over two hours, officials said.

After the Regina Caeli, Leo is expected to greet delegations and guests, the Vatican said.

Among the guests expected in attendance are Vice President JD Vance, wife Usha Vance and Secretary of State Marco Rubio.

Leo, formally Cardinal Robert Prevost, was elected the 267th pontiff on May 8. The Chicago native is the successor of Pope Francis, who died on April 21.

Leo started to emerge as a front-runner for the papacy in the days before the start of the conclave, according to the Rev. James Martin, a papal contributor to ABC News.

The new pontiff was the only U.S. cardinal on a short list of potential candidates for pope, also known as “papabiles,” compiled in the aftermath of Francis’ death by The Associated Press.

ABC News’ Phoebe Natanson and Christopher Watson contributed to this report.