An estimated 250,000 pilgrims from around the world filled the square as the Chicago-born pontiff, formerly Cardinal Robert Francis Prevost, was installed as the 267th successor to St. Peter.

The Mass, rich in tradition and symbolism, followed his election on May 8 following the death of Pope Francis.

The liturgy began with a solemn procession to the tomb of St. Peter, where deacons retrieved two sacred symbols of papal authority: the fisherman’s ring and the lamb’s wool pallium.

As Pope Leo XIV arrived in the popemobile, he was greeted by enthusiastic crowds, waving flags and chanting prayers.

In his homily, the 69-year-old pope called for peace, unity, and moral responsibility in an age of global instability and technological disruption.

“The Church must be a beacon of hope, a bridge between enemies, and a defender of justice in an age of rapid change,” he said.

The Mass drew a high-profile audience, including U.S. Vice President JD Vance, Ukrainian President Volodymyr Zelenskyy, Canadian Prime Minister Mark Carney, Israeli President Isaac Herzog, and Britain’s Prince Edward.

A former missionary in Peru and a trained mathematician, Pope Leo XIV is expected to continue the legacy of his predecessor with a strong focus on outreach to the marginalized, while also engaging with modern issues such as technology, global conflict, and climate change.

The Vatican confirmed that the pope will remain active on social media, maintaining a public presence aimed at younger and international audiences.

Pope Leo XIV will take possession of the remaining major papal basilicas in the coming days, beginning with St. Paul Outside the Walls on May 20. His first general audience is scheduled for May 21, followed by a meeting with Vatican Curia officials on May 24.