A federal appeals court in New York cleared the way on Tuesday for the city to release hundreds of thousands of police disciplinary records, a major milestone in a long and bitter political battle to open the records to public scrutiny.

The ruling by a three-judge panel, which also affects firefighters and corrections officers, dealt a heavy blow to efforts by officers’ unions to block the records’ release.

The decision was hailed as a victory by New York City as well as by civil liberties groups, which have long argued that making the materials public would make it harder for problematic officers to escape significant punishment.

Mayor Bill de Blasio, a Democrat, said his administration would move swiftly to release the records, though he did not give a time frame. “We look forward to releasing this data,” he said, adding the city would seek “clarity from the court” regarding when that could happen.

For decades, the disciplinary records of police officers in New York were shielded from public disclosure by the state’s civil rights law. Then, in June, the State Legislature repealed the section of the law, known as 50-a, that had kept such records confidential.

The repeal was part of a package of legislative changes aimed at reducing police misconduct in the wake of the killing of George Floyd at the hands of Minneapolis police officers, which had ignited nationwide protests against police brutality.

“For the past seven years, we’ve fundamentally changed how we police our city, strengthening the bonds between communities and the officers who serve them,” Mr. de Blasio said in a statement on Tuesday.

“Now, we can go even further to restore accountability and trust to the disciplinary process,” he said. “Good riddance to 50-a.”

Hank Sheinkopf, a spokesman for the coalition of unions that had sued to block the records’ disclosure, said the group was still considering its options and whether to pursue further appeals.