So who is the man asking the questions - and what does he have in store?
Lester Holt's CV includes major network shows such as Dateline NBC, Today, and his current role as anchor of NBC Nightly News, which attracts millions of viewers every night.
That makes him a national celebrity, and well used to high-stakes TV.
He has already been accused of political bias, when Mr Trump labelled him a Democrat and complained about the "unfair system".
But journalists checked voter records, and it turns out Holt is actually a registered Republican.
However, with more interest in presidential politics than ever, Monday night's debate is poised to be a major national event.
Some are predicting it could attract 80 or even 100 million viewers - well over 10 times Holt's usual audience.
Holt also finds himself at the centre of a row about just what a moderator should - and should not - do.
Earlier this month, a fellow NBC journalist, Matt Lauer, failed to challenge Mr Trump's false statement that he opposed the war in Iraq - which led to a huge backlash, and a debate on how much fact-checking a moderator should do.
Then, over the weekend, multiple news organisations published variations on a story, fact-checking hundreds of statements from both candidates.
The New York Times, Washington Post, and LA Times all accused both candidates of false statements - but each concluded that Mr Trump exaggerated or told untruths more frequently. Politico said Mr Trump's mishandling of facts "so greatly exceed [Mrs] Clinton's as to make the comparison almost ludicrous".
Mrs Clinton's campaign is calling for more fact-checking. Mr Trump wants the moderator to let the candidates fight it out themselves.
The truth - or lack of it - is a major issue in the campaign heading into the first debate, and Lester Holt will have to decide to what extent he challenges candidates on their statements.
Frank Fahrenkopf, the chair of the commission which organises the presidential debates, told the BBC that it is not the primary responsibility of the moderator to challenge perceived inaccuracies in what is essentially a debate rather than an interview.
"The candidates must work against each other," he said.
"If Donald Trump says something that's not right it's up to Mrs Clinton to correct it and vice versa."
"But if something is said that's blatantly wrong and goes uncorrected by the other party then the moderator has a difficult route to go.
"But they're not to be the judge, they're not to be the decider - that's what the debate is about - both parties are supposed to go at each other and the public will decide which one they are going to support."
Mr Fahrenkopf said that one thing is almost certain at the end of the debate - whoever loses is likely to blame the moderator.
Only three topics have been announced for the 90-minute debate: America's direction," "achieving prosperity" and "securing America".
None of that tells us very much - but the remaining questions will be based on current events. And in his role as news anchor, Mr Holt has already interviewed both candidates and put tough questions to each.
"Secretary Clinton, you famously handed Russia's foreign minister a reset button in 2009," Holt asked Hilary Clinton earlier this year.
"Since then, Russia has annexed Crimea, fomented a war in Ukraine, provided weapons that downed an airliner and launched operations, as we just did discuss, to support Assad in Syria. As president, would you hand Vladimir Putin a reset button?"
And Mr Trump hasn't had an easy time of it with Mr Holt either. "You made some very bold claims ... that didn't stand up," he said after Mr Trump claimed Hillary Clinton was asleep during an attack on an American compound in Benghazi.
Then, he proceeded to ask for evidence of Mr Trump's claim that Mrs Clinton's email server had been hacked - which Mr Trump could not provide.
Denounced no matter what
As the debate has drawn closer, Lester Holt has found himself on the receiving end of analysis from fellow journalists.
Broadly, he has received the backing of his peers - but some doubt he will escape unscathed.
"I don't envy Lester Holt. No matter what he does in the first presidential debate, he'll be denounced," a columnist wrote in the Washington Post.
At NPR, David Folkenflik wrote: "surely an anchor such as Lester Holt does not abdicate his duties as a truth-seeker and a journalist by serving as a debate moderator."
And writing for CNN, Dylan Byers said "he is one of the most focused and hardworking personalities in television news, with 35 years' experience and, in all that time, not a controversy to speak of."
But with the heated rhetoric on both sides of the campaign, Holt could find himself in the centre of a controversy no matter what he does.