Celebrating the event in Rome at a mass attended by about 7,000 poor people at St. Peter's Basilica, the Pope urged people not to ignore poverty by believing that "it's not my business, it's the fault of society".
"We have the talents, we are talented in the eyes of God. Consequently, no one can think that he or she is useless, so poor as to be incapable of giving something to others," he said.
He added that a lifetime of "doing nothing wrong isn't enough. Because God isn't an inspector looking for unstamped tickets".
To mark the day, Francis had lunch with about 1,500 destitute people inside the immense Paul VI Hall, which adjoins the Vatican Basilica and usually hosts papal audiences and conferences, while another 2,500 were fed elsewhere.
"I'm not ashamed to be poor, I'm even proud of it when I see the solidarity and generosity that I saw today, with all those arms stretching out to take care of our little ones," said Maria Lorena, who has nine children, and was among the guests.
"We are materially poor but rich in our faith and dignity," she added.
A chef in charge of official Vatican meals prepared the meals including gnocchi, veal bites with vegetables and tiramisu.
"I am happy seeing all these people here but we must not just help them for a day, but throughout the year," said Francesco, in his 50s, from Sardinia.
"A day like this gives a little hope, we hope for good things for the future."
The guests came from Italy, but also from France, Poland, Spain, Belgium and Luxembourg, with similar initiatives held in other dioceses across Italy and elsewhere in the world.
The pope has often spoken about social inclusion, indirectly criticising governments that do not pay attention to those on the margins of society.