Zohran Mamdani is set to take over as New York mayor at midnight local time, taking his oath of office at an abandoned subway stop, as the city's first Muslim mayor.
His office says the understated venue for the oath-taking reflects his commitment to working people, after the 34-year-old Democrat campaigned on promises to address the soaring cost of living.
But it remains to be seen if Mr Mamdani - virtually unknown a year ago - can deliver on his ambitious agenda, which envisions rent freezes, universal childcare and free public buses.
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.
What US President Donald Trump does could be a decisive factor.
The Republican, himself a New Yorker, has repeatedly criticised Mr 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 that 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 Mr Trump wages an expanding crackdown on migrants across the United States.
Mr 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 Mr Mamdani, whom he called a "communist lunatic."
The mayor-elect has said he believes Mr Trump is a fascist.
Mr Mamdani's private swearing-in at midnight to start his four-year term will be performed by New York Attorney General Letitia James, who successfully prosecuted Mr Trump for fraud.
A larger, ceremonial inauguration is scheduled for tomorrow with speeches from left-wing allies Senator Bernie Sanders and Congresswoman Alexandria Ocasio-Cortez.
Around 4,000 ticketed guests are expected to attend the event outside City Hall.
Mr Mamdani's team has also organised a block party that it says will enable tens of thousands of New Yorkers to watch the ceremony at streetside viewing areas along Broadway.
The new job comes with a change of address for Mr Mamdani as he swaps his rent-controlled apartment in the borough of Queens for the luxurious mayor's residence in Manhattan.
Some had wondered if he would move to the official mansion given his campaigning on affordability issues. Mr Mamdani said he is doing so mainly for security reasons.
Born in Uganda to a family of Indian origin, Mr Mamdani moved to New York at age seven and enjoyed an elite upbringing with only a relatively brief stint in politics, becoming a member of the New York State Assembly before being elected mayor.
Compensating for his inexperience, he is surrounding himself with seasoned aides recruited from past mayors' offices and former US president Joe Biden's administration.
Mr Mamdani has also opened dialogue with business leaders, some of whom predicted a massive exodus of wealthy New Yorkers if he won. Real estate leaders have debunked those claims.
As a defender of Palestinian rights, he will have also to reassure the Jewish community of his inclusive leadership.
Recently, one of his hires resigned after it was revealed she had posted anti-Semitic tweets years ago.
