Sanders was with his wife, Jane, who said Pope Francis was joined by Argentine Bishop and Chancellor of the Pontifical Academy of Sciences, Marcelo Sanchez Sorondo. A spokesman for the Vatican confirmed the meeting and said they spoke about foreign policy and climate change before the pontiff headed to the Greek island of Lesbos to see a refugee camp.
"He is a beautiful man," the presidential hopeful said. "I am not a Catholic, but there is a radiance that comes from him. It was very wonderful to meet him."
His wife, a Catholic, said "the trip was definitely worth it."
Sanders had attended a conference on social, economic and environmental issues hosted by the Pontifical Academy of Social Sciences on Thursday.
Pope Francis downplayed the meeting, saying he saw Sanders outside Santa Marta, his residence, and they exchanged hellos.
"When I came out he was there, he was staying at Santa Marta and knew at what time I would be leaving. I greeted him and his wife, a handshake and nothing more. It’s called courtesy," the pope said while returning to Italy from his trip to Lesbos. "If someone thinks that greeting someone is meddling in politics it's time to look for a psychiatrist."
Sanders, who often talks about his admiration for the Pope in speeches and his writing, said he believed Pope Francis was "one of the great leaders in modern world history."
"I just conveyed to him my admiration for the extraordinary work he is doing raising some of the most important issues facing our planet and the billions of people on the planet and injecting the need for morality in the global economy," he said.