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.
Polls are now closed in California, where voters are weighing in on a ballot initiative, "Proposition 50," to determine if the state will adopt a new congressional map that redraws five districts to be more Democratic-leaning, potentially allowing Democrats to flip them in the midterms.
Senate Minority Leader Chuck Schumer, a New Yorker who consistently declined to say if he would endorse Democratic candidate Zohran Mamdani for mayor of New York City, wrote in a post on X late Tuesday, "I congratulate @ZohranKMamdani on his well-earned & historic victory. We have worked together on a number of vital issues — like delivering historic debt relief for taxi drivers. I look forward to building on that partnership to keep NYC strong, fair, more affordable & thriving."
-ABC News' Oren Oppenheim
In his concession speech in the New York City mayoral race, former New York Gov. Andrew Cuomo said his campaign was the "right fight to wage."
"I am proud of what we did and what we did together," he said. "This campaign was to contest the philosophies that are shaping the Democratic Party, the future of this city and the future of this country."
He said it's notable that "almost half of New Yorkers did not vote to support a government agenda that makes promises that we know cannot be met."
He said his campaign was "a caution flag that we are heading down a dangerous, dangerous road. Well, we made that point, and they heard us, and we will hold them to it."
Cuomo thanked New York City Mayor Eric Adams for suspending his campaign "to make us more competitive," saying it was a "very gracious thing to do."
He also offered his congratulations to Zohran Mamdani, who is projected to win the mayoral race, which elicited boos from the crowd. Cuomo quickly chastised the reaction, saying, "That is not right, and that is not us."
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
