Walz, 60, a liberal governor and former high school teacher, and Vance, 40, a bestselling author and conservative firebrand senator, will portray themselves as sons of America's Midwestern heartland but polar opposites on the issues gripping the US
Walz has called his Republican opponents "weird" and Vance has come under fire for past comments disparaging some Democrats as "childless cat ladies".
Kamala Harris was widely viewed as the winner of her debate with Donald Trump. (AP PHOTO)
Aides to the two men expect fireworks during the 90-minute debate at the CBS broadcast centre in New York as they defend themselves and speak up for the candidates at the top of each ticket, Democratic Vice President Kamala Harris and Republican former president Donald Trump.
Harris and Trump are expected to watch the televised debate, which begins at 9pm Tuesday (0100 GMT on Wednesday), and Trump said he would offer a play-by-play commentary of the event on social media.
Harris was widely viewed as the winner of her debate with Trump on September 10 in Philadelphia, which was watched by an estimated 67 million people.
That square-off did little to change the trajectory of an extremely close election battle.
While Harris has edged ahead in national polls, most surveys show voters remain fairly evenly divided in the seven states that will decide the November election.
Democrat Tim Walz is seeking to introduce himself to voters who might not be familiar with him. (AP PHOTO)
With no more debates planned, however, the stand-off will allow Walz and Vance to make closing arguments on behalf of their campaigns - just as early voting ramps up across the country.
Each will fling mud.
Walz, who has sought to cultivate a homespun image as a former high school football coach, is expected to get Vance to defend his 2021 comments criticising Harris and other Democrats as "a bunch of childless cat ladies who are miserable at their own lives".
Walz is also likely to go after Vance for spreading a fictional story of Haitian immigrants eating household pets in Springfield, Ohio, a false claim that Trump has repeated and that local officials say has drawn bomb threats.
The Democrat will seek to introduce himself to US voters who might not be familiar with him while aiming to keep the conversation focused on Harris's agenda, a Walz adviser said.
Trump advisers said Vance could be expected to try to force Walz to defend the Biden-Harris administration's policies on immigration and the economy, as well his handling of the riots in Minneapolis in 2020 after the death of George Floyd, a Black man, at the hands of a white policeman.
Vance will also bring up questions about Walz's military service, said Tom Behrends, a retired command sergeant major who joined a Trump campaign call about the debate.
Republican vice presidential nominee JD Vance has held mock debates as part of his preparations. (AP PHOTO)
Republicans have accused Walz of exaggerating his final rank in the Army National Guard, where he served for 24 years.
Walz has in the past described himself as a retired command sergeant major, one of the highest non-commissioned officer positions in the army.
While he achieved that rank, he did not meet the requirements to retire with that title.
Vance, a former Marine who served as a military journalist, was deployed to Iraq but never saw combat.
Walz has been preparing for the debate with US Transportation Secretary Pete Buttigieg standing in for Vance while Vance tapped Tom Emmer, a US congressman from Minnesota, to stand in for Walz during mock debates.
Despite Vance having written "Hillbilly Elegy" - a popular 2016 memoir - US voters have a negative view of him, Reuters/Ipsos polling shows, with 51 per cent of registered voters saying they view him unfavourably, compared with 39 per cent who view him favourably.
That's a contrast with Walz, who 44 per cent of registered voters view favourably, with 43 per cent reporting an unfavourable view in the September 20-23 poll.
