"Courage means doing everything we can to prevent other parents from having to endure that loss," he said.
Alluding to her disappointment in Congress' failure to pass gun control legislation last week, Giffords called for courage from lawmakers.
"I believe we all have courage inside," she said. "I just wish there was more courage in Congress."
"It's been a hard two years for me," Giffords said, "but I want to make the world a better place more than ever."
Kelly also praised his wife.
"There are people who make things happen. There are people who watch things happen. And there are people who wonder what just happened," Kelly said. "Gabby Giffords is a person who makes things happen."
Kennedy cited Giffords' strength to carry on a difficult fight.
"Our family is still suffering from the heartbreak caused by gun violence," Kennedy said. "No one should have to lose a husband, a wife, a father, a child, to senseless murder.
"But as our nominee has shown, out of that pain and tragedy, we must find the strength to carry on, to give meaning to our lives, and to build a more just and peaceful world."