Senator John Edwards is due to be formally elected the Democratic Party's candidate for US vice-president on the third day of the convention in Boston.
Edwards was chosen as Kerry's running mate earlier this month
Mr Edwards, who was John Kerry's main rival for the presidential nomination, will also make the day's key speech.
He is expected to focus on the "big themes", said his wife, Elizabeth.
After the speech, a roll-call of US states will be held to nominate Mr Kerry to challenge George W Bush in the elections being held in November.
Mr Kerry arrived in his hometown on Wednesday in spectacular fashion, taking a boat across the harbour surrounded by veterans from the war in Vietnam.
"No retreat, no surrender," he vowed a day before he wraps up the convention with an acceptance speech supporters hope will boost his standing.
Despite an eloquent endorsement of Mr Kerry from former President Bill Clinton on Monday, the latest poll suggested a decline in voter support for the White House challenger.
Vice-President Dick Cheney said on Tuesday that on one of the main issues of the campaign - Iraq - voters would be better off re-electing Mr Bush.
Mr Cheney said both Mr Kerry and Mr Edwards had voted for the Iraq war, but against subsequent funding for the troops.
"We need a president who will back our troops 100%, and that's exactly what we've got in George W Bush," he said.
Republicans were preparing to release an 11-minute video on Wednesday with quotes from Mr Kerry tracing his thoughts on the war.
'Two Americas' theme
John Edwards made an early morning visit to the convention centre testing the microphone and joking: "Should I go ahead and give the speech now?"
Mr Edwards will be talking "both about the big themes of this campaign and optimism searching for a better tomorrow that this nation has always represented," his wife Elizabeth told CBS's The Early Show programme.
He is expected to repeat his assertion that George Bush has created "two Americas" - one for the rich and one for everyone else - reports say.
John Kerry said he was "ready to go, pumped up"
And he is set to salute Mr Kerry as a "decisive, strong" commander in chief due to his experience in Vietnam, according to prepared remarks reported by AP news agency.
His aides say it will be an unusual speech - focusing on the positive - rather than an attack on the Bush administration.
The senator for North Carolina is considered a charismatic speaker - reaching out to the hearts of Americans in a way Mr Kerry finds difficult, says the BBC's Justin Webb in Boston.
His speech will be carried live on the main US television networks and there will be intense interest in seeing whether his charm has worked, our correspondent says.
Also due to speak on the third day of the convention are Al Sharpton and Florida Senator Bob Graham, who both ran for the Democratic nomination.
John Kerry arrived in Boston after six days of campaigning across US states.
"Welcome home. Welcome to the Super Bowl," Mr Kerry told reporters in the back of his plane after it landed in Boston.
He said he felt "great, ready to go, pumped".
His acceptance speech on Thursday night would be a "surprise", he said.
Tuesday's speakers focused on praising Mr Kerry's leadership skills.
His wife, Teresa Heinz Kerry, said her husband was a leader who could "return America to its moral bearings".
Mrs Heinz Kerry, who was a Republican until two years ago, emphasised her husband's military service in Vietnam, and said his presidency would make the world a safer place.