Judge Nicholas Garaufis gave his findings Friday following a civil trial last month in Brooklyn. The Justice Department had sued on behalf a black fraternal organization.
The judge's memo says despite progress on diversity in recent recruiting, the Fire Department of New York hasn't committed enough time or resources to reverse a long history of discrimination against blacks. He's expected to spell out a remedy in a separate ruling.
The FDNY announced last month that nearly half of the people who signed up for its next exam are minorities. Currently, only about 3 percent of firefighters are black.
A city lawyer said Friday that the findings were being reviewed.