Leo raised existential questions about scientific progress, life and human rights during his opening speech to President Emmanuel Macron and diplomats at the Elysee Palace.
Given the wars plaguing Europe and the Middle East, he reaffirmed the Vatican's opposition to nuclear weapons and said the nuclear deterrence doctrine was "mistaken" since it was just fuelling a new arms race.
"Peace is not a balance of power; rather, it is built day by day through dialogue and justice," he said on Friday.
Leo arrived in Paris at the start of four intense days in France, where the Catholic Church has lost ground on influencing ethical issues given the strict approach to secularism that is enshrined in the French constitution.
Church bells across France tolled when Leo's charter flight landed at Paris's Orly airport, and upward of a million people are expected to turn out to see him during his visit.
The welcome has underscored the surprising level of interest in Leo's visit, the first by a pope in 18 years.
Later on Friday, Leo was to deliver a speech at UNESCO headquarters, celebrate vespers at the newly reopened Notre-Dame cathedral and then preside over a massive youth vigil at the Paris stadium Friday night.
Macron's office said Friday's meeting with Leo would provide an opportunity to discuss global challenges such as climate change and artificial intelligence, along with European and international affairs.
The talks are also expected to address end-of-life care and the protection of children.
Leo seems keen to emphasise Europe's Christian roots and try to push the church's message about the value and dignity of human life in a country where the right to abortion was enshrined in the constitution in 2024 and where MPs recently gave final approval to a bill allowing adults with incurable illnesses to receive lethal medication.
The French Catholic hierarchy strongly opposed the measures, in keeping with Catholic teaching that human life must be protected and defended from conception until natural death.
But the French hierarchy has lost much of its influence amid the secularising trends at play across Western Europe as well as a credibility crisis stemming from France's reckoning with its legacy of clergy sexual abuse.
The Pope will meet a small group of French victims of abuse by Catholic clergy on Sunday in Lourdes.
France had put in place Olympic-level security measures, including mounted police, bomb disposal experts, anti-drone measures and counter-terrorism measures, police said.
In Paris alone, plans called for 14,000 police officers, gendarmes, and military personnel and 2500 firefighters on Friday.
On Saturday, when Leo celebrates mass at the central Place de la Concorde, the numbers are only slightly lower.
with Reuters
