Calling Kerry - the Democratic challenger to President Bush in the November presidential election - a "good man, a great senator, a visionary leader", former US President Bill Clinton said only he could show Americans the way to a safer, more prosperous world.
At the convention, meant to confirm Kerry's nomination as the Democratic candidate for the November elections, Clinton on Monday capped a star line-up of speakers that also included former President Jimmy Carter and ex-vice president Al Gore.
"Tonight I speak as a citizen, eager to join you here in Boston as a foot soldier in the fight for our future, as we nominate a true New England patriot for president," Clinton said.
Though frail, the 80-year-old Carter was vocal in criticising President Bush.
"Truth is the foundation of our global leadership, but our credibility has been shattered and we are left increasingly isolated and vulnerable in a hostile world," Carter said.
"Without truth, without trust, America cannot flourish."
Bush's decision to launch a war in Iraq came in for a special roasting. Carter said the United States "cannot lead if our leaders mislead" and said Bush's agenda had polarised the country.
"You can't be a war president one day and claim to be a peace president the next, depending on the latest polls," Carter said.
Gore, who lost the 2000 election to Bush after a bitter recount dispute in Florida that was settled by the Supreme Court, said the battle should inspire Democrats working to put Kerry in the White House in November.
"To those of you who felt disappointed or angry with the outcome in 2000, I want you to remember all of those feelings," Gore said. "But then I want you to do what I have done - focus them fully and completely on putting John Kerry and John Edwards in the White House."