Leo travelled to the eastern city of Metz, near the border with Luxembourg and Germany, to honour Robert Schuman, a French Catholic statesman regarded as one of the founding fathers of European unity after World War II.
Leo decided to end his four-day visit to France in Metz, at a conference centre named for Schuman, to drive home his appeal.
The American pontiff wants Europe to draw from its Christian foundations and traditions to respond to Russia's war in Ukraine and other conflicts.
"Over the past 80 years, Europe has amply demonstrated that it is possible to articulate divergent opinions, claims and interests through encounter rather than conflict," he said on Monday.
"We need to commit ourselves to patient dialogue, to show courage in negotiation and to be willing to give up some positions for the greater good of peace."
The Elysee Palace, the French presidential office, had invited all European Union heads of state and the heads of European institutions to attend the conference, but only a handful joined President Emmanuel Macron, from smaller states such as Monaco, Andorra and Luxembourg.
Leo's visit to the once staunchly Catholic and officially secular France has been marked by his appeal for Europe to remember its Christian heritage and apply it to today's ethical and geopolitical challenges.
On Sunday at the Catholic shrine in Lourdes, he condemned legislation - recently approved in France - permitting medically assisted dying, calling it immoral "false compassion".
Huge crowds have met him at nearly every turn - 800,000 attended Leo's Mass on Paris' iconic Place de la Concorde - surprising even organisers.
In his final event in France, Leo will celebrate mass in the cathedral of St Stephen in Metz later on Monday.
Schuman is best known for the Schuman Declaration of 1950, five years after World War II ended.
It proposed the creation of a European Coal and Steel Community to pool production between historical rivals France and Germany.
The idea, as Europe was emerging from the ruins of the war, was guided by the belief that intertwined economic interests would make another conflict between them "not merely unthinkable, but materially impossible".
The coal and steel organisation was the first among European institutions that were precursors to what eventually became the European Union.
Schuman, a resistance fighter imprisoned by the Nazis, was declared "venerable" in 2021, a step in the Catholic Church's process towards possible sainthood.
Leo praised especially Schuman's respect for international law in pursuing his idea of peaceful integration.
It was an indirect reference to how Russia's invasion of Ukraine, as well as US military incursions in Venezuela and the Iran war, have taken place outside the international legal order.
Leo said international law and multilateralism "constitute the best antidote to the desire for domination, which lies at the root of every conflict".
He lamented that in its place, relations today between states are becoming "increasingly uncivilised".
