He offered a candid critique of Republicans, calling the tea party "crazy," according to a detailed readout of Biden's remarks provided to CNN by a person in the room.
"This is not your father's Republican Party," he said, according to the source. "This is a different breed of cat, man. I am not making a moral judgment, but I will tell you that they have no judgment."
Biden was in South Carolina for the day to support local Democrats in competitive races. But South Carolina's role as an early presidential primary state added another layer of political intrigue to his trip, one of several to the state this year.
His office declined to comment on his remarks at the private meeting.
Biden predicted dire consequences for Democrats if Republicans win full control of Congress in November.
"If they win again, we are going to get no consensus on anything for the next two, four, six years," Biden told the gathering of more than 100 ministers. "But if we beat some of these folks, it's going to give some spine to the Republicans who know better."
He added, "If we win, will turn things around. There will begin to be consensus."
The day's public event was a rally at Allen University, a historically black university in Columbia. Before a crowd of roughly 1,000 people, Biden took sharp aim at Republicans in Congress and in the South Carolina state house, including Gov. Nikki Haley, accusing them of putting ideology over compromise.
"Your governor is denying 200,000 South Carolinians additional Medicaid because she opposes expansion," Biden said.
But he was more blunt in the gathering with ministers. He said Americans side with Democrats on issues from minimum wage, "tax fairness," combating climate change and making climate change affordable. Pointing to the enactment of strict voter ID laws in GOP-dominated states, Biden said Republicans have been successful in discouraging Democrats, especially African-Americans, from voting.
"What the other team has done so skillfully over the last 15 years is convince our folks that it's not worth voting," he said. "Rich guys never get fooled that it's not worth voting. They always show up and vote. But they tell our folks it doesn't matter, that government doesn't work anyway."
At one point referring to himself as "Joe Biden, progressive Democrat," Biden pointed to gains in manufacturing jobs under President Barack Obama, but said the middle class still "has not come back yet."
"You can see it in the eyes of your parishioners," he said. "It's not just in black America, it's white America as well. People are wondering, when is it going to be OK?"
"Corporate profits have soared," Biden said, criticizing "these guys running hedge funds in New York." He noted that the top 1% of earners in the United States make almost a quarter of all the money earned in the country. "How can that possibly be fair?" he asked.
"The biggest problem is income inequality," he said, echoing populist-themed remarks he made at a South Carolina fundraiser earlier this year. "Because when income inequality spreads, economies shrink because folks don't have money to spend."
Sitting next to South Carolina Rep. Jim Clyburn, the highest-ranking African-American in Congress, Biden talked up his political background and told the assembled audience that he "got 98% of the African-American vote every time I ran" in Delaware.
Black voters routinely make up a majority of the Democratic primary electorate in South Carolina.
Biden pointed out that his career began as a young public defender in Delaware, representing low-income clients. That's when he called himself "the only white boy on the east side of Wilmington."
Later in the day, Biden echoed his remarks at a fundraiser for the South Carolina Democratic Party at the home of Dick Harpootlian, a prominent local attorney and former state party chairman. About 40 people attended, including Elizabeth Colbert-Busch, the sister of comedian Stephen Colbert, who unsuccessfully ran for Congress last year.
"He gave a great speech," Harpootlian said. "He said Republicans are being stymied by the extremists John Boehner that doesn't want to go against. He said that hopefully some moderates can prevail this November."
Harpootlian, who has been publicly critical of Hillary Clinton, said Biden will have a head start in South Carolina if he decides to run for president because of his previous campaigns and his longtime friendship with former Sen. Fritz Hollings.
"If he runs, there is no candidate who will have been to South Carolina as many times as he has," Harpootlian said. "He has a built-in infrastructure."