A New York City panel voted on Thursday to freeze rents for nearly one million rent-stabilized apartments, fulfilling one of Mayor Zohran Mamdani’s key campaign promises and handing the mayor a major policy win six months into his tenure.

The panel, known as the Rent Guidelines Board, approved the freeze on both one- and two-year leases in a 7-to-1 vote, pausing increases on more than 40 percent of all apartments across the five boroughs — a mix that includes high-rise luxury apartments, deeply affordable subsidized units and 150-year-old walk-ups. New York City now may offer a model for rent control efforts in other cities and states.

“This is a historic victory for New York City tenants,” Mr. Mamdani said in a statement after the vote. He added, “I’ll continue working to deliver a more affordable city by building and preserving affordable housing, lowering building operating costs like insurance and ensuring tenants know their rights.”

The freeze would apply to leases beginning on or after Oct. 1. It was the first rent freeze ever on both one- and two-year leases.