"If you like the Bush/Cheney approach, John McCain's your man. If you want change, then vote for Barack Obama and Joe Biden," Gore said.
Bernice King and Martin Luther King III, the slain civil rights leader's daughter and son, both spoke. Bernice King, a minister, said the Democrats had picked a nominee "not by the color of his skin but by the content of his character. This is one of our nation's greatest defining moments."
"On this 45th anniversary of the march on Washington, and in honor of the legacies of my father and Bobby Kennedy, let us elect a leader who has heard the clarion call," Martin Luther King III said.
Supporters at the stadium earlier Thursday anxiously looked forward to Obama's address.
"I would sit in the bathroom here and listen to him over the radio," said Rosa Maria Chavez, 26, an alternate delegate from Lakewood, Colo. who was seated four rows from the top of the stadium. "Just knowing I'm this close is a thrill."
Meanwhile, McCain's spokesman said the presumptive Republican nominee would appear Friday with his yet-to-be-named running mate in Dayton, Ohio. McCain also released a commercial in which he congratulates Obama.
"Too often the achievements of our opponents go unnoticed, so I wanted to stop and say congratulations," McCain says in the ad. "How perfect that your nomination would come on this historic day.
"Tomorrow, we'll be back at it. But tonight, senator, job well done."
Contributing: Associated Press