Last winter, Eileen Kelley received a notice that her landlord was not going to renew her lease when it expired in a few months. After eight years in the East Village, a neighborhood in Manhattan she had come to love for its street markets and parks, Ms. Kelley, 29, confronted the sudden possibility that she might have to leave.

But scrolling through TikTok just before her lease ended, she found a video that introduced her to a new, renter-friendly law called “good cause eviction.” Passed by New York State last spring, the legislation prohibits landlords from forcing renters out of their homes just because their lease term is over.

The law felt like it could be a lifeline. Ms. Kelley, who works in financial services, told her landlord that she wasn’t going to leave. After months of back and forth over email, she finally received a new lease, securing her apartment until at least this coming September.

“I was like, ‘Wow, the system does work for us,’” she said.

The exchange is one example of how the law is quietly reshaping parts of New York City’s housing market. Renters are challenging landlords, both in informal lease negotiations and in court, to secure breaks on rent and new leases. Property owners say they are growing cautious about trying to get even troublesome renters out, and they worry about other consequences of what they see as government overreach.

“It gives tenants a little more confidence in their rights,” Ms. Kelley said, adding that she has shared her experience with friends. “A lot of people didn’t realize that the lease renewal is even negotiable.”

The law’s rollout comes as public anger over the city’s housing crisis is increasingly pushing politicians to tackle the high cost of living. Many proposals have focused on making it easier to build more homes to address a housing shortage that is at its worst point in half a century.