The Next Leader of a Key N.Y.C. Business Group? He’s From New Jersey.

The Partnership for New York City, an influential business advocacy group, announced on Monday that Mayor Steven Fulop of Jersey City would take over the organization as its next leader.

The role has been held for more than two decades by Kathryn S. Wylde, a power broker who has shaped mayoral administrations, public policy and the influence of New York’s business class.

Ms. Wylde announced in May that she would step down after the partnership had found a replacement, ending a career there that began in 1982, a few years after David Rockefeller formed the group as a voice of the business community following New York City’s fiscal crisis.

Today, the partnership represents more than 300 companies, including some of the biggest firms in finance, media, real estate and technology like Google, JPMorgan Chase and Verizon. Collectively, the companies employ more than a million people in the city.

Mr. Fulop will become the organization’s president and chief executive early next year, just after his third term as mayor ends.

In public and behind the scenes, Ms. Wylde, 79, has warned of anti-business rhetoric that she says drives away development and jobs, and she has championed the benefits of the city’s corporate giants and their wealthy business leaders, including the taxes they pay.

In an interview on Tuesday, Mr. Fulop defended those business leaders, saying: “People like to villainize them but they are conscious, aware, thoughtful, invested in the future of New York City, and they want to see New York City do great for everybody.”

Mr. Fulop, a Democrat, has been the mayor of Jersey City, the state’s second largest city, since 2013. One stop away from Lower Manhattan on the PATH commuter train, the city has added about 45,000 residents since he became mayor, during a wave of new housing construction.

On Sept. 11, 2001, Mr. Fulop was working in Lower Manhattan and saw the first plane slam into the World Trade Center. He quit his job as an analyst at Goldman Sachs and enlisted in the Marines.

Mr. Fulop will take over the partnership at an uncertain time for the city and its business community. President Trump has increasingly targeted New York, his former hometown, with federal funding cuts. He tried to kill congestion pricing in Manhattan, which Ms. Wylde has defended, and suggested he might send in the National Guard.

Business leaders are also preparing for the possibility that Zohran Mamdani, the Democratic front-runner for mayor, could be elected next month as one of the most left-leaning mayors New York has seen in decades.

Mr. Mamdani has promised to make the city more affordable with four signature policies, including universal child care, that would cost $7 billion a year. He has proposed paying for them with higher taxes on wealthy residents and corporations.

Asked after the Democratic primary in June about the business community’s opinion of Mr. Mamdani, Ms. Wylde said, “Terrified.”

Over the summer, Mr. Fulop defended one of Mr. Mamdani’s major plans — trying to bring down the price of groceries by opening five city-owned supermarkets. Mr. Mamdani’s idea “isn’t as fringe as some might assume,” he wrote in a social media post, adding that “exploring solutions isn’t a bad thing.”

He started off the post by making one point clear — Mr. Fulop proudly lived on the other side of the Hudson River: “I don’t live in NYC nor do I want to.”

But now?

“This time next year, I will be a New York State resident and a New York City resident,” he said.