How Zohran Mamdani beat Andrew Cuomo

Instead, the city overwhelmingly voted for Zohran Mamdani, a formerly little known Queens assemblyman and self-described socialist, in one of the city’s biggest political upsets in decades.

Political observers say the 33-year-old triumphed over Cuomo and the Democratic establishment by building a strong ground game, piling up grassroots donations and rallying voters worried about affordability.

Mamdani was omnipresent on TV and social media and filmed videos with influencers and celebrities. Progressives coalesced around him after Rep. Alexandria Ocasio-Cortez and Vermont Sen. Bernie Sanders endorsed him.

“He was fresh while everybody appeared tired," said political consultant Hank Sheinkopf.

More than a million door knocks

Mamdani had an astounding rise from February, when he was polling at 1% to former New York Gov. Cuomo’s 33%. On Monday this week, polling suggested Mamdani would trail Cuomo for the first seven rounds of ranked-choice voting before prevailing in the eighth.

By Wednesday, Mamdani had racked up more than 43% of the vote to Cuomo’s 36%, with most votes counted, according to the city elections board. The official outcome of the race will still be determined by a ranked-choice vote count.

Cuomo conceded the race less than two hours after the first results came in.

The speed with which Mamdani toppled his rival Tuesday night surprised even his own team. “We felt very good going into last night. We did not anticipate it was going to be that early," said senior adviser Zara Rahim.

Assemblyman Mamdani wasn’t widely known outside his Queens district but benefited from word-of-mouth support in the last stretch of the race.

The candidate rallied young and left-leaning voters with promises to make buses free, invest $70 billion in publicly subsidized housing and freeze rents on rent-stabilized apartments.

Mamdani mobilized about 50,000 volunteers who knocked on roughly 1.6 million doors, according to his campaign team and Camille Rivera, a Democratic strategist who consulted for them.

Mamdani took to Instagram and TikTok with a mix of polished, produced videos and selfie-style takes. He also appeared on podcasts and “The Late Show with Stephen Colbert."

Rivera said Mamdani had a clear message and understood how to communicate that through his field work, social media and surrogates.

“He talked about affordability in a way people could understand," Rivera said.

Cuomo, a moderate, vowed to make subways safer and hire more police officers.

A growing base

An army of supporters coalesced behind Mamdani on his election-eve march down Manhattan last week. He gave out bro handshakes and took selfies on his 13-mile trek. Two young women told him they registered to vote so they could cast ballots for him.

Voters showed up by the hundreds of thousands at the ballot box: In electoral districts where at least 25% of residents had bachelor’s degrees, Mamdani often beat Cuomo, according to a Wall Street Journal analysis of election results and census data.

His wave, interviews show, was buoyed by hope among voters that Mamdani could lower costs in one of the world’s most expensive cities.

Mamdani performed extremely well with renters while homeowners favored Cuomo, according to John Mollenkopf, director of the Center for Urban Research at the CUNY Graduate Center.

Teresa Gonzalez, a Democratic campaign strategist, said Mamdani inspired voters who felt hopeless after Kamala Harris lost the 2024 presidential election. “Here comes this really young and charismatic person saying, ‘There is still hope for us here,’" Gonzalez said.

Ranked choice strategy

In the second New York City mayoral election using ranked-choice voting, Mamdani harnessed a successful strategy.

The Working Families Party encouraged four progressive candidates—Mamdani, city comptroller Brad Lander, City Council Speaker Adrienne Adams and Brooklyn state Sen. Zellnor Myrie—to have their voters rank all four. Several of the candidates cross endorsed each other and steered votes away from Cuomo. “We could not afford to have our side divided," said Ana María Archila, a co-director of the party in New York who helped devise the cross-endorsement strategy.

Cuomo never found a blueprint to overcome the “Don’t Rank Cuomo" tactic for his comeback to politics. In 2021, he resigned as governor after facing sexual-harassment allegations he has denied.

Cuomo’s opponents encouraged voters to use the ranked-choice system to pick anyone but him, with Mamdani hoping to be the top beneficiary.

In a ranked-choice election, voters can list up to five candidates in order of preference. A candidate needs more than 50% support to win. If no one hits that minimum, the candidate with the fewest votes will be eliminated. The ousted candidate’s votes are redistributed to the voters’ second choices. In 2021, Eric Adams won after several rounds.

What’s next

Mamdani is widely expected to clinch the official nomination next week when the city finishes counting mail-in ballots. He will then face off against several contenders in November’s general election.

That field is expected to include Curtis Sliwa, the Republican nominee who ran unopposed in the primary, independent Jim Walden, and current New York City Mayor Adams. Adams opted to sit out the Democratic primary and has said he wants to run in November under party lines he created: “Safe&Affordable" and “EndAntiSemitism."

Cuomo’s future in the race remains unknown. The former governor could re-enter the general election under his separate party line, Fight and Deliver—but it isn’t yet clear if he will want to.

Sheinkopf, the political consultant, said it is unlikely Cuomo would return to face Mamdani in November.

“It wasn’t a small beating," he said. “He got killed."

Write to Alyssa Lukpat at alyssa.lukpat@wsj.com, Victoria Albert at victoria.albert@wsj.com and Jack Gillum at jack.gillum@wsj.com