The day after an Uzbek man killed eight people and wounded 12 others in Manhattan near the 9/11 Memorial, Mayor Bill de Blasio maintained the celebrated event would go on, vowing: "We will not be cowed. We will not be thrown off by anything."
The city is heavily bolstering security for the race, parking more sand trucks to prevent vehicle attacks, stationing extra police on rooftops and deploying more anti-sniper units.
In addition to uniformed officers along the route, plainclothes officers will blend in with the spectators.
Security had already been boosted in 2013 after the Boston marathon attack that saw two youths of Chechen descent plant two bombs near the arrival line, killing three people and wounding more than 250 others, including spectators.
The Islamic State group has described Sayfullo Saipov -- the 29-year-old man charged with driving a rented pickup truck down a bike path in Manhattan as children and their parents prepared for Halloween -- as one of its own, prompting President Donald Trump to call for his execution.
Sunday's marathon will serve as a means for New Yorkers to come together in defiance in the aftermath of the latest attack to strike America's most populous city.
- 'Opportunity to show resilience' -
The race that takes runners through all five boroughs and culminates at Manhattan's iconic Central Park will be a show of "resilience" for a city recovering from tragedy.
"What I do know, 100 percent, is that we're a very resilient nation and I don't think there are many tougher people than New Yorkers, and marathoners are pretty tough too," said American runner Shalane Flanagan, the 2008 Olympic silver medallist over 10,000m.
"So I think it's an opportunity to show resilience and strength and coming together... And when you come together as a community it really empowers people and helps people heal."
Flanagan said the carnage in New York had hit her hard as a veteran of the 2013 Boston marathon.
"It's obviously devastating and very concerning," she said of the New York attack.
"I've been in a terrorist attack in 2013 in Boston. I was there that day and had just completed my race. So it very much hits home and is very personal to me having been a part of a terrorist attack."
Flanagan said she may consider retiring if she stuns the field with a victory on Sunday.
Standing in her way is defending champion Mary Keitany of Kenya, who is chasing a fourth consecutive victory in New York.
In the men's race, Kenya's former world record holder Wilson Kipsang, who won the 2014 edition of the event, and last year's winner Ghirmay Ghebreslassie of Eritrea are among the favorites this time around.