Manhattan DistrictJudge Shira Scheindlin cites "overwhelming evidence" that the program "has led to thousands of unlawful stops."
Scheindlin's ruling also said the city's "cavalier attitude towards the prospect of a 'widespread practice of suspicionless stops' displays a deeply troubling apathy towards New Yorkers' most fundamental constitutional rights."
"The vast majority of New Yorkers who are unlawfully stopped will never bring suit to vindicate their rights," the ruling said. "It is precisely for cases such as this that [the class action law] was designed."
The stop and frisk program has been vigorously defended by Mayor Michael Bloomberg as having saved more than 5,000 lives, the New York Post reported.
"I think as of today -- we're 135 days into the year -- I think we've had 135 murders," Bloomberg said in a news briefing. "If it were to stay at this rate, you would have 50 percent less than when we came into office."
City Council Speaker Christine Quinn lauded Scheindlin's ruling, calling it "an important step towards the systemic reform of this practice."
The New York Police Department declined to comment.