Mamdani urged the city to "breathe this moment in."
Democrats triumphed in high-profile races that unfolded across the country on Tuesday, including New York City's mayoral election and governor's races in New Jersey and Virginia.
In California, voters also chose to redraw their state's congressional map in a move that could net Democrats five House seats.
The elections help provide a picture of how Americans feel about President Donald Trump's first nine months in office. Following a wave of Republican losses, Trump tried to blame the election results on his not being on the ballot and the prolonged government shutdown.
The Democratic National Committee is arguing that tonight’s results are indicative that the youth vote is back on their side.
They argue that exit polling indicates they've "successfully won back" voters aged 18-29 while pointing to exit polls regarding young voters in the gubernatorial races in Virginia and New Jersey and the mayoral race in New York City.
-ABC News' Brittany Shepherd
Republican mayoral candidate Curtis Sliwa offered an emotional concession speech to supporters Tuesday night, stressing that the movement he built on the backs of the Guardian Angels, focused on creating a safer New York, will not be erased.
He also said his candidacy was proof that voters cannot be bought or bullied by the establishment, as he was pressured to drop out of the race to clear the field for independent Andrew Cuomo.
"This has always been us versus them. From the time I declared my candidacy, the masters of the of the universe, the billionaires decided that I should not have the right to represent all of you to be the voice of the voiceless, the working class people who the backbone of this city," said Sliwa. "You can't buy us, rent us. We are not for sale. We are the people."
Sliwa offered good luck to Zohran Mamdani, who is projected to win the mayoral election. Though he warned that if Mamdani tries to "implement socialism" or weaken police, Sliwa and his coalition will become the Mamdani administration's "worst nightmare."
-ABC News' Brittany Shepherd
After coming out on stage to New Jersey son Bruce Springsteen's "Born to Run," Mikie Sherrill made a promise of prosperity during her victory speech in the state's gubernatorial race.
"Liberty alone is not enough if the government makes it impossible for you to feed your family, to get a good education or to get a good job," she said. "So in this country, that shouldn't be too much to ask, but right now, all of it seems at risk. Governors have never mattered more, and in this state, I am determined to build prosperity for all of our citizens."
Sherrill said it was a "tough fight," and that she had just gotten a call from her opponent, Republican Jack Ciattarelli.
"I want to recognize him for stepping up," she said.
Affordability is the key theme in all of tonight's major races. And it’s clear why -- the typical American household is spending $208 extra per month right now on the same goods and services compared to this time last year because of inflation, according to Moody’s Analytics.
Households are spending $1,043 per month more now compared to the start of 2021 coming out of the pandemic.
-ABC News' Elizabeth Schulze
