The Argentine pontiff arrived at the Martyrs stadium around 9:00 am local time (0800 GMT), offering greetings and blessings to the crowd roaring in the stands.
Young people had already begun to flock to the 80 000-seat stadium overnight, with many hoping for a papal message of peace for the Democratic Republic of Congo, a deeply observant country which has long been plagued by violence in its east.
About 60% of the central African nation of roughly 100 million people is under the age of 20, according to UN figures.
As well as conflict, young people face persistent unemployment in the DRC.
Sheila Mangumbu, 21, said she was hoping for a "message of peace" from Francis, especially for residents of the eastern city of Goma.
M23 rebels, allegedly backed by Rwanda, have captured swaths of territory in eastern DRC since late 2021 and come within kilometres of the commercial hub of Goma.
"The M23 is killing many of us in the east. I would like this to stop because it has been going on for too long," Mangumbu told AFP.
On the second day of his trip, the pope hosted a mass at Kinshasa's airport that organisers said drew about a million people, some of whom had camped out all night to get a spot.
He then met victims of conflict in the DRC's mineral-rich east, some of whom have suffered appalling violence.
His face grave, Francis called for mercy from God.
"May he convert the hearts of those who carry out brutal atrocities which bring shame upon all humanity," he said.
He said the conflict was being driven by greed and called on combatants to lay down their arms.
"Listen to the cry of their blood," the pope said, alluding to a verse from the Book of Genesis.
Scores of armed groups roam eastern DRC, many of them a legacy of two wars at the end of the 20th century that sucked in countries from around the region.
The DRC is replete with minerals, timber and fresh water, yet remains one of the poorest countries in the world where corruption is entrenched.
Shortly after his arrival from Rome on Tuesday, the pope – speaking before an audience of Congolese politicians and other dignitaries – said the DRC had been hamstrung by a long history of exploitation.
"Political exploitation gave way to an economic colonialism that was equally enslaving," he said.
"As a result, this country, massively plundered, has not benefited adequately from its immense resources."
Many Congolese warmly welcomed the pope's message, and some hoped it would bring change.
After addressing the young people at Martyrs Stadium, the pope will later meet Jesuit leaders and priests on the frontline of the church's work in the DRC.
About 40% of the country's population is Catholic, according to official statistics, and the church retains huge influence despite secularism being enshrined in the constitution.
Francis will take his appeal for peace and reconciliation to South Sudan tomorrow for a maiden three-day visit.
Born in 2011 after gaining independence from Sudan, the nation has been battered by civil conflict that has left around 380 000 dead.
The visit to the two countries was initially scheduled for 2022 but had to be postponed because of the pope's problems with his knee – an affliction that has made him dependent on a wheelchair.
It is his 40th foreign trip since he ascended to the papacy in 2013.
Agence France-Presse