Jan. 1 Day 1

Mr. Mamdani took the oath of office at a midnight ceremony in the abandoned City Hall subway station, surrounded by family. On New Year’s Day, he was sworn in by Senator Bernie Sanders on the City Hall steps, in front of masses of rosy-cheeked New Yorkers bundled against the cold, cheering under a flurry of confetti.

Jan. 2 Day 2

On his second day in office, he created an Office of Mass Engagement, a reflection of the way an army of volunteers aided his mayoral campaign, with more than 100,000 people knocking on three million doors and making 4.5 million calls to talk to voters. He put the office in the hands of Tascha Van Auken, who served as Mr. Mamdani’s campaign field director and previously worked for former President Barack Obama’s 2008 campaign

Jan. 3 Day 3

Mr. Mamdani called President Trump to criticize the strikes in Venezuela, after New Yorkers awoke to the startling news that the U.S. military had seized Venezuela’s president, Nicolás Maduro.

Jan. 4 Day 4

Mr. Mamdani, who had promised to help people with bad landlords, announced a series of “rental rip-off” hearings, where renters from every borough could come and meet with city officials to talk about their landlord headaches. Standing in a building on Sedgwick Avenue credited with being the birthplace of hip-hop, the mayor unveiled a series of moves aimed at supporting tenants — a key political class that makes up nearly 70 percent of New Yorkers, and a group that Mr. Mamdani strategically tapped into as he was running for mayor.

Jan. 5 Day 5

Mr. Mamdani and Gov. Kathy Hochul’s relationship was still looking tenuous at the start of his term. But the two looked chummy when they came together to celebrate the one-year anniversary of the embattled congestion pricing program, which had come under attack from President Trump.

Jan. 5 Day 5

Mr. Mamdani announced that he would pause sweeps of homeless encampments, while he re-evaluated the way they were conducted under his predecessor, Eric Adams. Before taking office, he had been a critic of heavy-handed approaches to serving the city’s homeless population.

Jan. 6 Day 6

Mr. Mamdani tested out a favorite phrase — “no issue too small” — as he stood surrounded by workers in hard hats and paved over “the bump,” a notorious pit at the foot of the Williamsburg Bridge.

Jan. 7 Day 7

Mr. Mamdani hosted a “new media” briefing, touring influencers around City Hall. It was a friendly audience for the mayor, with one beauty influencer offering Mr. Mamdani a sentiment he’s unlikely to hear from the traditional press corps: “I have had so much fun making content for you.”

Jan. 8 Day 8

The mayor stood together with Ms. Hochul to announce a plan to expand child care options for nearly 100,000 young children. Affordable child care was a centerpiece of Mr. Mamdani’s campaign to ease the burden of heavy expenses that so many New Yorkers face.

Jan. 10 Day 10

Mr. Mamdani announced he would commit $4 million to install at least two dozen modular toilets across the five boroughs. When the mayor talked about “sewer socialism” during his run for office, few knew that he would take the term literally.

Jan. 12 Day 12

On a cold Monday morning, the mayor moved on up from Astoria, Queens, to the Upper East Side, home to Gracie Mansion, the official mayoral residence. Reflecting on his home in Astoria, Mr. Mamdani said he and his wife, Rama Duwaji, would miss the Adeni chai and smell of shawarma on his old block.

Jan. 13 Day 13

Mr. Mamdani made his first return to Albany since taking office. The trip in a motorcade, surrounded by aides, was a capsule of the transformation he had undergone in one head-spinning year. When he’d driven up to Albany as a state assemblyman, he used to ride shotgun with a colleague and sing show tunes.

Jan. 16 Day 16

One of the mayor’s first acts to help renters was to have the city intervene in the bankruptcy case of a large landlord, Pinnacle, which was facing thousands of complaints from tenants across the city. But a federal judge ruled that Pinnacle’s sale of 5,000 apartments to Summit Realty, another landlord facing complaints, could proceed over the city’s objections, an early challenge to the mayor’s efforts to help renters.

Jan. 25 Day 25

As snow fell, Mr. Mamdani blitzed local news, sent out plows to clear streets and disappointed children by announcing there would be virtual school, though he told everyone they could pelt him with snowballs. For every mayor of New York City, snowstorms serve as a major test. The 1969 blizzard became known as the “Lindsay snowstorm” because it paralyzed the city, and voters blamed the mayor, John Lindsay. So Mr. Mamdani knew that his response to the oncoming storm would be closely watched.

Jan. 27 Day 27

A bitter cold snap that followed the snowstorm proved a greater challenge. The death count from the freezing weather rose to at least 10 people by Jan. 27. The Mamdani administration sent outreach workers scouring the streets for people exposed to the elements, scrambling to bring vulnerable people indoors.

Feb. 5 Day 36

In a disappointment to some members of his progressive base, Mr. Mamdani endorsed Ms. Hochul for re-election on Feb. 5, strengthening their alliance but potentially losing leverage in his efforts to persuade her to raise income taxes on the rich.

Feb. 12 Day 43

For all Mr. Mamdani’s sweeping promises while running for office, his administration was quickly marked by a clear willingness to make some compromises. He backtracked on CityFHEPS, one of the largest rental assistance programs in the nation. Mr. Mamdani said he no longer intended to back the growth of the more than $1 billion initiative, because of the competing need to address the city’s budget deficit.

Feb. 12 Day 43

Mr. Mamdani, maestro of the stunt, surprised the city’s romantics by showing up at City Hall to wed couples there, two days before Valentine’s Day.

Feb. 15 Day 46

Mr. Mamdani announced that he was forming a new business improvement district in Coney Island, with a first-year budget of up to $1 million.

Feb. 17 Day 48

Mr. Mamdani presented his preliminary budget, addressing the $5.4 billion hole he has to fill by the time the spending plan takes effect July 1 — a shadow hanging over his ambitious affordability agenda. He warned that property tax rates in New York City might be raised by nearly 10 percent if he could not persuade Ms. Hochul to raise income taxes on high earners.

Feb. 18 Day 49

Emerging from weeks when criticism over his handling of homelessness escalated during the city’s cold snap, Mr. Mamdani announced that he would begin sweeping homeless encampments again. But the sweeps would look different than they did under Mr. Adams, and would be led by the Department of Homeless Services rather than the Police Department.

Feb. 20 Day 51

Mr. Mamdani announced that the city would crack down on employers that might be violating worker protection laws. This enforcement push came days before a new law took effect expanding time off protections for more than five million New Yorkers. Mr. Mamdani and his administration started the enforcement push, sending warning letters to 56,000 companies.

Feb. 23 Day 54

As another snowstorm began, the Sanitation Department went into a full force mobilization: Plows went block to block, 2,600 emergency workers headed out for 12-hour shifts and pay was raised for emergency snow shovelers. A total of 19.7 inches of snow fell in Central Park, placing it in the city’s top 10 storms dating back to 1869 — more than enough to persuade the mayor to declare a full snow day for school children.

Feb. 23 Day 54

A snowball fight was held in Washington Square Park on the afternoon of the blizzard. The event turned chaotic when police officers arrived and were hit with snowballs, which Police Commissioner Jessica Tisch called “disgraceful” and “criminal.” The mayor was less perturbed, suggesting that throwing a snowball should not result in criminal charges. The police later arrested a man in connection with the snowball fight; prosecutors declined to bring assault charges.

Feb. 25 Day 56

Hundreds of protesters, led by groups including the Democratic Socialists of America, gathered in Albany for a rally calling for raising taxes on the rich. Mr. Mamdani skipped the event. He has done a delicate dance since taking office, trying to ensure that the progressive organizers who put him in office feel that their voices are heard, while also working to maintain relationships with power brokers like Ms. Hochul.

Feb. 26 Day 57

In his second meeting with President Trump at the White House, Mr. Mamdani brought a mock cover of The Daily News, a play on the infamous “Ford to City: Drop Dead,” with the new headline: “Trump to City: Let’s Build.” There are few relationships in America as eyebrow-raising, perplexing, amusing and ripe for analysis as the buddy-comedy-ready duo of Mr. Mamdani and President Trump. One is a democratic socialist, the other the Make America Great Again kingpin. Both are also sons of New York City who have mastered the attention age.

March 3 Day 62

Mr. Mamdani announced that he had chosen four areas in New York City in which to begin his child care expansion, with 2,000 seats in the 2-K program set to open up this fall.

March 5 Day 64

The Mamdani administration announced it would close the homeless shelter in the former Bellevue psychiatric hospital, which was well known among many New Yorkers seeking a place to sleep but had also fallen into disrepair.

March 6 Day 65

Mr. Mamdani was questioned about a handful of instances in which his wife, Ms. Duwaji, had liked posts appearing to celebrate Hamas’s deadly attack on Israel, right after Oct. 7, 2023. He declined to criticize the posts or address his wife’s actions, saying that she is “a private person who has held no formal position on my campaign or in my City Hall.”

March 7 Day 66

Chaos arrived on Mr. Mamdani’s doorstep. A far-right provocateur, Jake Lang, was gathering his followers outside Gracie Mansion for a protest called “Stop the Islamic Takeover.” Two men who had expressed support for the Islamic State were arrested after one was seen hurling a homemade bomb into the protest. The device did not detonate, and no one was injured.

March 9 Day 68

Mr. Mamdani appeared sober-faced outside his residence on Monday morning, two days after the bomb incident. He stood alongside Ms. Tisch and denounced the attempt at violence while also condemning the “display of bigotry” at the protest. Ms. Tisch said the throwing of the devices was being investigated as an act of “ISIS-inspired terrorism.”

March 11 Day 70

Mr. Mamdani showed up in person at a “rental rip-off” hearing in the Bronx, even meeting with three tenants who had complaints about roaches, broken elevators and safety. He also faced protests from some New Yorkers who live in public housing and reminded the mayor that he is actually New York’s largest landlord.

March 17 Day 76

Mr. Mamdani sought a judge’s approval to stop representing the former mayor, Mr. Adams, in a sexual assault lawsuit that had been filed in 2024. The mayor has tried, throughout his first 100 days in office, to distance himself from his predecessor.

March 17 Day 76

Mr. Mamdani not only marched in the St. Patrick’s Day Parade in Manhattan, but also gave a speech drawing a parallel between Irish history and the Palestinian struggle for self-determination.

March 19 Day 78

Mr. Mamdani signed an executive order creating an Office of Community Safety, which will begin with just two staff members and a far narrower scope than he had pledged.

March 20 Day 79

Mr. Mamdani infused the holy month of Ramadan with spirit, breaking his fast with different groups every day. He shared iftar meals with firefighters, incarcerated people at Rikers and delivery drivers, as well as stopping at some of his favorite restaurants. For New York’s more than half a million observant Muslims, this year marked a poignant shift, the first time a person who shared their faith was running the city and observing Ramadan at City Hall.

March 24 Day 83

Mr. Mamdani announced settlements with two companies that would provide nearly $2 million to more than 800 fast food and retail workers, including at Dunkin’ and Taco Bell, who had been the victims of “Fair Workweek” violations. A livestream of the announcement also included him eating a Crunchwrap Supreme.

March 25 Day 84

As the Mamdani administration grapples with the looming budget deficit, the mayor gave a quick snapshot of some of the ways the city planned to cut $1.7 billion in spending, including by cutting contracts with consultants and auditing the health care eligibility of dependents. Behind the scenes, the administration quietly identified another $1.3 billion in potential savings from scaling back programs Mr. Mamdani had endorsed on the campaign trail.

March 30 Day 89

Mr. Mamdani attended a Passover Seder at City Winery in Lower Manhattan, seeming unbothered by hecklers as he addressed a crowd that included George Floyd’s brother, Al Franken and Don Lemon, who read the Four Questions.

April 7 Day 97

The Mamdani administration announced the opening of a rest stop for delivery workers, which had been in the works for years but was sped to completion in the first 100 days of the administration.

April 7 Day 97

Mr. Mamdani selected Rebecca Jones Gaston, who as head of child welfare under former President Joseph R. Biden Jr. oversaw the expansion of abuse-prevention services for families, to lead the city’s Administration for Children’s Services.

Ms. Jones Gaston previously oversaw child welfare in Maryland and then in Oregon, where she released a “vision for transformation” that stated that “white supremacy and systemic racism are deeply embedded in the history, fabric and institutions of our country, including child welfare systems.”