And he added: "I pledge to you that I will be there next January on the floor of the United States Senate."
That had special meaning given the bleak prognosis Kennedy faces with his disease.
"The hope rises again and the dream lives on," he said after his seven minutes at the microphone, minutes of high and unexpected drama for delegates waving thousands of Kennedy signs, cheering as he came and as he stepped away into the arms of his wife, Vicki.
"My fellow Democrats, my fellow Americans, it is so wonderful to be here," he said. "And nothing, nothing is going to keep me away from this special gathering ..."
Kennedy flew to Denver Sunday night, and his first stop was a hospital, where doctors examined him. His physicians had been wary of the trip, especially his exposure to crowds, given the weakness of his immune system after weeks of chemotherapy and radiation treatments. The brain cancer was diagnosed after he collapsed in May in Hyannis Port, Mass. After brain surgery in June, he had remained at home, save for a brief trip to Washington to cast a Senate vote on July 10 for Medicare legislation that had been stalled in deadlock.
It was to have been a Kennedy appearance on tape, after a tribute by his niece, Caroline Kennedy. But he came himself, and his performance, if brief, was not frail. "I have come here tonight to change America, to restore its future, to rise to our best ideals and to elect Barack Obama president of the United States," he said.
Kennedy's speech would have been standard convention fare, nothing remarkable, but for his health. It was a striking performance for a man of 76, stricken by cancer. "As I look ahead, I am strengthened by family and friendship," he said. "So many of you have been with me in the happiest days and the hardest days.
"Together we have known success and seen failure ... victory and defeat," he said. He said this is the time for victory, for the election of Obama. "For me this is a season of hope ... new hope ... and this is the cause of my life, new hope that we will break the old gridlock ..."
In introducting him, Caroline Kennedy said her uncle "has been a senator for all who believe that the dream has never died." She said "Uncle Teddy" and Obama are "two men who have changed my life and the life of this country.
"Leaders like them come along rarely," she said. "But once or twice in a lifetime, they come along just when we need them the most This is one of those moments."
She said that in this campaign, Obama "has no greater champion" than Kennedy. "When he is president, he will have no stronger partner in the United States Senate," she said.
Before Kennedy's dramatic appearance at the Pepsi Center in Denver, CBSNews.com caught up with one of Kennedy's longtime colleagues, Rep. Barney Frank, D-Mass.
"It's bittersweet," Frank said of the video tribute to Kennedy. "It's a tribute to a man who is very ill, who has been just an incredible force for all of the things that the people at this convention care about. And it's great to be able to see him again, and it's sad to know he's ill."