Leo is spending four intense days in Paris, the Catholic shrine at Lourdes and the northeastern city of Metz.
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.
Leo was greeted by President Emmanuel Macron at the airport and will meet again at the Elysee Palace.
During his busiest day of the trip, Leo was to then 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.
For Macron, who is barred from seeking a third term in May elections, hosting the American pope is something of a capstone after Pope Francis refused repeatedly to make a proper state visit to France during his 12-year pontificate.
With seven months left in his term, Macron's approval ratings are near record lows, driven by anger over the rising cost of living and criticism of France's growing debt and deficit and deteriorating public services.
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 also are 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 has 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
