New York, New York - Zohran Mamdani was sworn in at midnight on Thursday to take over as New York City mayor.

After the clocks struck midnight, bringing in 2026, Mamdani took his oath of office at an abandoned subway stop to begin managing the nation's largest city. He is New York's first Muslim mayor.

His office said the understated venue beneath City Hall reflected his commitment to working people, after the 34-year-old Democrat campaigned on promises to address the soaring cost of living.

"This is truly the honor and the privilege of a lifetime," Mamdani told reporters after taking his oath.

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The 34-year-old won over voters with an ambitious agenda, which envisions rent freezes, universal childcare, and free public buses. Now, it will be up to the new mayor and his administration to deliver.

Once an election is over, "symbolism only goes so far with voters. Results begin to matter a whole lot more," New York University lecturer John Kane said.

How Trump behaves could be a decisive factor. The Republican, himself a New Yorker, has repeatedly criticized Mamdani, but the pair held surprisingly cordial talks at the White House in November.

Lincoln Mitchell, a political analyst and professor at Columbia University, said the meeting "couldn't have gone better from Mamdani's perspective."

But he warned their relationship could quickly sour.

One flashpoint might be immigration raids as Trump wages an expanding crackdown on migrants across the US.

Mamdani has vowed to protect immigrant communities.

Before the November vote, the president also threatened to slash federal funding for New York if it picked Mamdani, whom he called a "communist lunatic."

The mayor-elect has said he believes Trump is a fascist.

Mamdani's private swearing-in to start his four-year term was performed by New York Attorney General Letitia James, who successfully prosecuted Trump for fraud.

A larger, ceremonial inauguration is scheduled later Thursday with speeches from political allies Senator Bernie Sanders and Congresswoman Alexandria Ocasio-Cortez.

Around 4,000 ticketed guests are expected to attend the event outside City Hall.

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Mamdani's team has also organized a block party that it says will enable tens of thousands of people to watch the ceremony at streetside viewing areas along Broadway.

In a first for the city, Mamdani is using several Korans to be sworn in as mayor – two from his family and one that belonged to Puerto Rico-born Black writer Arturo Schomburg, The New York Times reported.

The new job comes with a change of address as he swaps his rent-controlled apartment in the borough of Queens for the luxurious mayor's residence in Manhattan – a move Mamdani said he is making mainly for security reasons.

Born in Uganda to a family of Indian origin, Mamdani moved to New York at age seven. He was first elected to the New York State Assembly in 2020 to represent the 36th district in Queens before being elected mayor.