Reuters reported that this was the only scheduled debate between the two candidates in the 2024 US presidential campaign - a crucial moment in a fierce competition.
The nationally televised debate begins at 9 p.m. ET on Sept. 10. It comes just eight weeks before the Nov. 5 election and days before early voting begins in some states.
Former President Donald Trump said he would contrast the left-wing policies Ms Harris proposed during her unsuccessful 2020 presidential campaign with the more centrist positions she has identified now.
For her part, Ms. Harris said she would focus on attacking Mr. Trump’s habit of lying. “Donald Trump has a real problem with the truth,” Ms. Harris wrote in a social media post on the morning of September 10. Her campaign released an ad featuring former President Barack Obama mocking Mr. Trump’s false claims about the size of crowds at his events.
Kamala Harris will also talk about her plan to cut everyday spending by Americans, according to campaign advisers.
The debate is particularly important for Ms Harris, as polls show more than a quarter of potential voters feel they still don't know enough about her.
The debate also gave Ms. Harris, a former prosecutor, a chance to make her case against Mr. Trump, a convicted felon who publicly supported supporters convicted in the attack on the U.S. Capitol on Jan. 6, 2021.
It will be the first time the two candidates have met and comes after weeks of personal attacks by Mr Trump and his allies on Ms Harris, including racist and sexist remarks.
Trump advisers and other Republicans have urged him to focus on high inflation and immigration that have plagued President Joe Biden’s tenure, even though both have fallen sharply this year.
"He's willing to talk about why your life is better when he's in office," Lara Trump, Trump's daughter-in-law, told CNN.
Presidential debates don’t necessarily change voters’ minds, but they can change the dynamics of the race. Biden’s poor performance against Trump in the June debate was so damaging that he ultimately dropped out of the race.
In a race that could come down to tens of thousands of votes in a handful of states, even a small shift in public opinion could change the outcome.
According to an average of polls compiled by The New York Times, Ms. Harris and Mr. Trump are essentially tied in seven battleground states that are likely to decide the election.
"Kamala Harris has more to gain and more to lose, because she is still less known to many voters," said Mitchell McKinney, a former adviser to the US Presidential Debates Committee.
Voters will be looking for her stance on a variety of issues. But just as importantly, they will be looking for how she presents herself against Mr Trump, who is already very popular.
The 90-minute debate, hosted by ABC News, will take place at the National Constitution Center in Philadelphia. By agreement between the campaigns, there will be no live audience and microphones will be muted when it is not a candidate's turn to speak.
