Mamdani has been sworn in as New York City’s mayor at an abandoned subway station beneath City Hall, beginning his term as the first Muslim to lead the United States’ (US) largest city.
His office said the understated location was deliberately chosen to reflect his commitment to working-class New Yorkers, a central theme of his campaign focused on tackling the rising cost of living.
“This is truly the honor and the privilege of a lifetime,” Mamdani told reporters after being sworn in.
His oath was administered by New York Attorney General Letitia James, who previously prosecuted President Donald Trump for fraud.
The ceremonial inauguration later Thursday is expected to feature speeches from Senator Bernie Sanders and Congresswoman Alexandria Ocasio-Cortez. Around 4,000 ticketed guests are set to attend the event outside City Hall.
Mamdani’s team has also organised a block party, allowing tens of thousands of people to watch the ceremony at designated viewing areas along Broadway.
Despite the symbolic opening, questions remain over whether Mamdani, virtually unknown a year ago, can deliver on an ambitious agenda that includes rent freezes, universal childcare and free public bus services.
“Once an election is over, symbolism only goes so far with voters. Results begin to matter a whole lot more,” said John Kane, a lecturer at New York University.
How President Trump behaves could prove a decisive factor. The Republican, himself a New Yorker, has repeatedly criticised Mamdani, though the two held unexpectedly cordial talks at the White House in November.
Columbia University professor and political analyst Lincoln Mitchell said the meeting “couldn’t have gone better from Mamdani’s perspective”, but warned the relationship could quickly sour.
Trump’s ongoing increase in raids targeting immigrants across the US makes immigration a possible flashpoint. Mamdani has promised to defend New York’s immigrant communities.
President Trump called Mamdani a “communist lunatic” and promised to stop federal funding for the city if he won the November election. Mamdani has described Trump as a fascist.
Mamdani took the oath with his hands on two copies of the Holy Quran — one belonging to his grandfather and the other from the New York Public Library’s Schomburg Centre for Research in Black Culture.
The new role also brings a change of address, as Mamdani moves from his rent-controlled apartment in Queens to the mayor’s official residence in Manhattan. He said the move was driven mainly by security concerns, despite questions raised during the campaign over affordability.
Born in Uganda to a family of Indian origin, Mamdani moved to New York at the age of seven. With a relatively brief political career that included serving in the New York State Assembly, he has sought to compensate by surrounding himself with seasoned aides from previous mayoral administrations and the government of former president Joe Biden.
He has also opened dialogue with business leaders, some of whom had predicted a mass departure of wealthy New Yorkers if he won. Real estate leaders have since dismissed those claims.