Kennedy, who is being treated for a malignant brain tumor, is a beloved figure within the Democratic Party, and the Massachusetts senator's last-minute appearance at the Pepsi Center is a way to unite the fractured party as the four-day convention opens amid signs of acrimony between Obama and Clinton delegates.
He plans to attend to watch a video tribute to him, though not address the convention.
"He's truly humbled by the outpouring of support and wouldn't miss it for anything in the world," said Stephanie Cutter, a Kennedy spokeswoman.
As Democrats put the final touches on opening night, Obama's campaign released an ad featuring images of McCain hugging Bush and the two smiling in spite of tidings of economic woe and McCain admitting he doesn't know much about the economy. "We can't afford more of the same," the spot warns.
McCain's campaign also released an ad to play on what it sees as a weakness for Obama: his lack of support among some backers of primary opponent Hillary Rodham Clinton. Its new TV ad features a Clinton supporter who now backs McCain assuring like-minded voters: "A lot of Democrats will vote McCain. It's OK, really!"
Opening night at the Pepsi Center, the main venue for the four-day convention, aimed to tell the Illinois senator's personal story to the millions of voters nationwide who will begin tuning in to the presidential campaign. Obama's wife, Michelle, was the evening's keynote speaker.