Both camps described the meeting as "positive" and said the two noted their shared commitment to stopping Trump and pursuing issues such as raising the minimum wage, eliminating undisclosed money in politics, making college affordable and making healthcare coverage more accessible.
Sanders spokesman Michael Briggs said the meeting was "a positive discussion about how best to bring more people into the political process and about the dangerous threat that Donald Trump poses to our nation."
Also attending were Sanders' wife Jane, Clinton campaign chairman John Podesta and the two campaign managers, Jeff Weaver for Sanders and Robby Mook for Clinton.
Sanders had promised to stay in the Democratic race until the final vote was cast in the Washington, D.C., primary, although in the past week he has stopped talking about capturing the party's nomination and instead focused on ways to advance his policy goals.
He scheduled a national video address to supporters on Thursday night, telling them in an email message that "the political revolution continues."
At a news conference before the Washington meeting, Sanders said he would also demand changes to make the Democratic nominating process more equitable, including replacing the Democratic National Committee leadership, letting independents take part in the voting and eliminating superdelegates, who are unelected and are free to support any candidate.
"The time is long overdue for a fundamental transformation of the Democratic Party," Sanders said.
Clinton easily beat Sanders in the District of Columbia, winning 79 percent to his 21 percent in a primary that closed the more than four-month, state-by-state battle for the Democratic nomination that began on Feb. 1 in Iowa.
During a visit to Capitol Hill earlier on Tuesday, Sanders told Democratic senators he would take his message of progressive values and party reform to the convention.
"I'm open to that, I think we should all be open to that," Senator Dick Durbin of Illinois told reporters afterward. "It's not a surprise that the American people are skeptical of all of us in political life. And we ought to step back and reassess why, and what we can do about it."
Top Democrats have taken steps in the last week to begin rallying behind Clinton and ease Sanders out of the race without alienating his supporters.
President Barack Obama endorsed Clinton on Thursday, hours after meeting with Sanders at the White House. Clinton also secured the endorsement of Senator Elizabeth Warren of Massachusetts, a leader of the party's progressive wing.
Clinton already has turned her attention on the campaign trail to the race with Trump, rejecting the New York businessman's renewed calls for a ban of the entry of foreign-born Muslims into the United States after the mass shooting at a gay club in Orlando, Florida, by an American man who claimed allegiance with Islamic State militants.
"I have clearly said that we faced terrorist enemies who use a perverted version of Islam to justify slaughtering innocent people. We have to stop them, and we will," Clinton said in Pittsburgh, Pennsylvania, on Tuesday. "But I will not demonize and declare war on an entire religion."