Crowds stretched the length of the Avenue des Champs-Élysées in Paris as Pope Leo urged Catholics to find happiness in faith, not material things.
The outdoor mass on Saturday was the biggest event of his visit to France, with an estimated 800,000 people attending, about 200,000 more than the number who had registered in advance.
Chants of "Leo, Leo" and "Long live the Pope" echoed down the roughly 2-kilometre tree-lined boulevard, from the Place de la Concorde to the Arc de Triomphe, as people pressed against security barriers for a glimpse of Leo as he arrived in an open-top Popemobile.
The vehicle paused frequently as Leo blessed people with disabilities, children and babies passed forward by volunteers.
Onlookers waved white and yellow Vatican flags.
Attendees included Brigitte Macron, the French president's wife, far-right leader Marine Le Pen, who is leading in the polls ahead of next year's presidential election, Prime Minister Sebastien Lecornu and Bernard Arnault, the billionaire chairman of French luxury group LVMH.
Cheers rang out in the crowd as Leo thanked God in his sermon for the chance to visit France on a whirlwind four-day, three-city tour, during which he is seeking to repair the church's standing after abuse scandals caused nationwide shock.
The pope told Catholics that only their faith would provide true happiness.
"Only God can fill the emptiness within us," the pope said.
The pope, who has forcefully decried the direction of global leadership in recent months, warned in a speech on Friday at the Paris headquarters of the UN culture and education body UNESCO, that the UN and other multilateral groups were in crisis.
He also repeated his frequent appeal for the world to reconsider the development of artificial intelligence, telling French leaders that AI could create a future where "a paradise of machines" takes control of the Earth.
He has frequently spoken out for peace, including in remarks with French leaders at the Élysée on Friday, with his comments criticising the Iran war earlier this year drawing a rebuke from US President Donald Trump.
Pope draws diverse crowd
Attendees began assembling before sunrise to hear the pontiff speak at the mid-afternoon mass.
Many on Saturday didn't identify as Catholics, but came to hear the pope's message.
"People are seeing a lot of really terrible images. This kind of event reminds people of what is really important in life," said Thierry Chen, a 40-year-old Parisian startup entrepreneur who is not Catholic.
Benoit Dedieu-Anglade, 67, said he was impressed by the pope's speech.
"We must not give in to the easy path or distractions — and I was moved by how he expressed this in such clear, lucid French," he told Reuters.
Pierre-Marie Estienne, 36, was in the crowd for Leo's mass in central Paris with his wife and their four young children.
"We live in an era of great materialism," he told Reuters before Leo arrived.
"There is a lot of evil around us, so we need a message of hope and love."
Pope visits newly baptised Catholics
France, a secular nation where the separation of church and state is enshrined in a 1905 law, has witnessed a steady decline in affiliation to the Catholic Church since World War II, mirroring a trend in other traditionally Catholic countries.
Although the French Bishops' Conference points to an increase in baptisms of adults, including a record 21,000 last Easter, a report published by the official statistics agency, INSEE, showed that only 25 per cent of French 18 to 49-year-olds identified as Catholic, compared with 43 per cent a decade earlier.
In a visit on Saturday with newly baptised Catholics at the Catholic University of Paris before the mass, Leo urged the French church not to be "naively optimistic" about the recent increase in adherents.
"We must recognise, welcome and protect the small flame that the Holy Spirit has kindled in the darkness of the night, the tiny seed that strives to grow even amid the thorns," he said.
After the open-air mass on Saturday, he headed to Lourdes in southern France, one of the Catholic church's most-visited shrines.
He will meet seven French victims of abuse by clergy there on Sunday.
