Zohran Mamdani was sworn in as New York City mayor in the first minutes of the New Year at the historic City Hall subway station, with his wife Rama Duwaji standing by his side.

The oath, in which he pledged to support the Constitution of the United States and the laws of New York, was administered by New York State Attorney General Letitia James as Mamdani placed his hand on the holy Quran.

"Happy New Year to New Yorkers, both inside this tunnel and above," said Mamdani, standing beneath a vaulted ceiling with the words City Hall over his head. "This is truly an honour and a privilege of a lifetime."

Mamdani was a trailblazing candidate and is expected by many in his city of 8 million -- some with hope, some with trepidation -- to be a disruptive mayor.

The democratic socialist's plans for his first day in office on Thursday nod to his politics and priorities, without straying far from his predecessors with a sober official midnight oath-taking followed by a more celebratory ceremony in the afternoon.

New York law spells out that four-year mayoral terms start on the January 1 after elections. To avoid any ambiguity about who's in charge of America's most populous city, it has become a tradition to hold a small swearing-in just after midnight.

Mamdani chose the Old City Hall subway stop, which was decommissioned in the middle of the previous century and is accessible only a few times a year through guided tours, as the site of his swearing in.

The subway site, according to Mamdani’s transition team, reflects his "commitment to the working people who keep our city running every day."

Mamdani, a 34-year-old former state lawmaker, promised a freeze on rents and free buses and childcare, building a campaign around affordability issues that some have seen as a path forward for his Democratic Party around the country ahead of midterm elections.

Mamdani inspired a record-breaking turnout of more than 2 million voters and took 50 percent, nearly 10 points ahead of Andrew Cuomo running as an independent and well ahead of Republican Curtis Sliwa.

Attorney General James was among his earliest prominent backers. During the first administration of President Donald Trump, James began investigating his business practices in New York, resulting in a judge finding in 2024 that Trump fraudulently overstated his net worth to dupe lenders.

The Trump administration has targeted James during his second term, accusing her of mortgage fraud.

Grant Reeher, a Syracuse University political science professor, said James's role in the inauguration would send a message to core supporters that Mamdani is "going to be independent of the president.”

Inauguration of a new era

The Uganda-born Mamdani, who will be New York City's first Muslim mayor, has been a sharp critic of Trump on issues such as immigration and said his differences with the president were numerous after a warm White House meeting.

But being sworn-in by the state attorney general may say more about Mamdani's political alliances than rivalries. In 2014 Bill de Blasio, whom Mamdani regards as the best New York City mayor of his lifetime, was sworn in privately by then-New York Attorney General Eric Schneiderman at the start of the first of his two terms.

Senator Bernie Sanders, a progressive, Brooklyn-born Vermont senator whom Mamdani calls his inspiration, presided over de Blasio's public inauguration ceremony in 2018 and will play a similar role for Mamdani. Liberal Democratic U.S. Representative Alexandria Ocasio-Cortez is also on the inauguration ceremony agenda.

Plans for Mamdani's public inauguration include a ceremony on City Hall's steps and a program of music and speeches in front of 4,000 guests gathered in City Hall Plaza. In addition, tens of thousands of people will be able to watch a livestream of what Mamdani's team has dubbed the “Inauguration of a New Era” in free viewing areas set up along Broadway.

Mamdani raised $2.6 million for the transition and celebrations from nearly 30,000 contributors, more than other mayors on record this century, both by the total and single donations, according to official campaign data that presents disclosures of inaugural expenses beginning with Michael Bloomberg's first term in 2001.

Sami Zaman, the owner of Astoria's low-key Afghan restaurant Sami's Kabab House, where Astoria resident Mamdani filmed a campaign video with Sanders, was on the inaugural committee alongside filmmakers, writers and activists.

After becoming mayor, Mamdani will move from his one-bedroom Astoria apartment, protected from sharp price hikes by the city rent-stabilization program, to Gracie Mansion, the official residence of New York City mayors on Manhattan's upscale Upper East Side.

Bankers and others in New York, the nation's financial capital, had expressed concern about Mamdani but since his election many have explored how to work with him.

The city has had another mayor associated with democratic socialism, David Dinkins. Dinkins did not make much of his association with the Democratic Socialists of America. During his 1990-1993 term he overcame budget deficits and persuaded private businesses to remain in New York, according to city archivists.