Emerging from the West Wing after more than 45 minutes, Sanders said he and Obama discussed domestic and foreign policy and "a little bit of politics."
The Vermont senator, who called the meeting "productive and constructive," said he expects Obama and Vice President Joe Biden to be "fair" to the Democratic presidential candidates during the primary, brushing off the suggestion that Obama is favoring his former secretary of state, Hillary Clinton.
Speaking to reporters after the meeting, Sanders reflected on Obama's 2008 performance in Iowa ahead of this year's caucuses.
"We're feeling really good about where we are, and if there is a large voter turnout -- I'm not saying we could do what Barack Obama did in 2008. I wish we could, but I don't think we can. But If there is a large turnout, I think we win,” Sanders said.
Sanders, who last met with Obama privately in December of 2014, acknowledged his disagreements with the president on trade and taxes, but said he has stood "by his side" in legislative battles on Capitol Hill against Republicans.
ABC News’ latest polling shows Clinton leading Sanders by 19 points nationally -- her smallest lead yet, with five days to go until the Feb. 1 Iowa Caucus. A new Quinnipiac poll of Iowa has Sanders moving ahead of Clinton with 49 percent support to her 45 percent.
“She’s extraordinarily experienced -- and, you know, wicked smart and knows every policy inside and out,” Obama said, unabashedly touting Clinton's readiness to be commander-in-chief. "It means that she can govern and she can start here, day one, more experienced than any non-vice president has ever been who aspires to this office."
As for Sanders, the president indicated the upstart contender entered the race "with the luxury of being a complete long-shot and just letting loose” as he introduced himself to voters.
“I've gotten to know Hillary really well, and she is a good, smart, tough person who cares deeply about this country, and she has been in the public eye for a long time and in a culture in which new is always better,” Obama said. “You're always looking at the bright, shiny object that people don't -- haven't seen before. That's a disadvantage to her. Bernie is somebody who -- although I don't know as well because he wasn't, obviously, in my administration -- has the virtue of saying exactly what he believes, and great authenticity, great passion, and is fearless. His attitude is, ‘I got nothing to lose.’”
The White House said the idea for the Sanders meeting came up in the photo line in December at the Congressional Ball, according to the White House. Sanders suggested then that it would be nice to have a more formal sit-down. It took a few weeks to get it on the calendar.
ABC News' Mary Bruce contributed to this report.