New York’s highest court on Thursday overturned the felony sex crimes conviction of the notorious Hollywood producer Harvey Weinstein, a staggering reversal of a bedrock case in the #MeToo era that prompted countless victims of sexual harassment and assault to come forward as accusers.

In a bitterly contested 4-to-3 decision, the New York Court of Appeals found that the judge who had presided over Mr. Weinstein’s case deprived him of a fair trial in 2020 by allowing prosecutors to call witnesses who said Mr. Weinstein had assaulted them — but whose accusations were not the basis for any of the charges against him.

Responding on Thursday, the Manhattan district attorney, Alvin L. Bragg, announced that he would seek to prosecute Mr. Weinstein again.

“We will do everything in our power to retry this case, and remain steadfast in our commitment to survivors of sexual assault,” a spokeswoman for Mr. Bragg’s office said. The case was originally prosecuted by his predecessor, Cyrus R. Vance Jr.

For Mr. Weinstein, 72, the immediate impact of the ruling might amount to little more than a change of scenery. He is likely to be transferred from the prison in Rome, N.Y., where he has been held since 2020, to a facility nearer to New York City, where he will await the filing of new charges. But the opinion also raised questions about whether a separate conviction in California — on rape and sexual assault charges — can survive a similar legal challenge.

That case, which saw Mr. Weinstein sentenced to another 16 years in prison in 2022, also relied in part on witnesses whose accusations did not lead to charges. Mr. Weinstein’s lawyer in the California case said she planned to file an appeal next month.

A representative of the Los Angeles County district attorney’s office said it was “saddened by the news out of New York.”

“Our office had representatives in New York during the trial, and we are aware of the extreme difficulties the victims faced while testifying about the traumas that Mr. Weinstein caused them,” the representative said, adding: “We are confident that our convictions will withstand appellate scrutiny.”

The decision to overturn the New York conviction, while shocking to many, had been anticipated in legal circles. The criminal case against Mr. Weinstein had been viewed as fragile since the day it was filed, and prosecutors were believed to have taken risky, boundary-pushing bets to see it through. Still, the ruling was met with expressions of shock and anger by some of Mr. Weinstein’s accusers.

Ashley Judd, the first actress to come forward with allegations against Mr. Weinstein, called it “unfair to survivors.”

“We still live in our truth,” Ms. Judd said on Thursday. “And we know what happened.”

Mr. Weinstein’s lawyer, Arthur Aidala, said his client learned of the decision when he was handed a news report on a slip of paper by someone in the prison facility.

“He said thank you more times than I can count,” said Mr. Aidala, who spoke to Mr. Weinstein by phone Thursday morning. “Harvey was very gracious, very grateful.”

The former producer’s health has been steadily declining in recent years. He has diabetes, eye problems and heart issues, has used a walker and was housed in a medical unit at the prison, the Mohawk Correctional Facility.

“He has been going through bouts of difficulty,” said a spokesman, Juda Engelmayer.

Mr. Weinstein had been a sharp-elbowed titan in the film industry, rising to power in the 1990s behind a stream of critically lauded, blockbuster movies under the Miramax label. His downfall after lurid accusations emerged from dozens of actresses and former colleagues became a primer for how the world viewed and treated many once-powerful men who used their positions for sex.

Mr. Weinstein was accused of sexual misconduct by more than 100 women. But in New York he was convicted of raping an aspiring actress, Jessica Mann, and assaulting a television production assistant, Miriam Haley, and sentenced to 23 years in prison. Thursday’s decision did not discount the credibility of the accusations against him. Rather, it found fault with the admission of the testimony of women whose descriptions of abuse fell outside the criminal case.

Prosecutors in sexual assault and other cases often seek to use them to establish a pattern of behavior. But doing so risks unfairly influencing the jury because the defendant is supposed to be judged only on the crimes he is charged with. For that reason, judges seek to limit such testimony, and the judge in Mr. Weinstein’s case, Justice James M. Burke, did not permit the prosecutors to call as many of those witnesses as they had hoped to. But he did allow a handful to testify.

The appeals court said that he should not have.

“It is an abuse of judicial discretion to permit untested allegations of nothing more than bad behavior that destroys a defendant’s character,” Judge Jenny Rivera wrote on behalf of the majority, “but sheds no light on their credibility as related to the criminal charges.”

Donna Rotunno, Mr. Weinstein’s lead trial lawyer in New York, praised the ruling on Thursday.

“They were prosecuting him for sins, not crimes,” she said. “This speaks to our justice system as a whole. The court ruling says to prosecutors: Winning at all costs is not your job. Your job is to put on a fair trial.”

The Court of Appeals also faulted the trial judge for permitting prosecutors to question the producer about uncharged allegations — spanning back decades — if he decided to take the stand. He did not testify.

Dawn Dunning, one of the women who prosecutors called to the stand even though Mr. Weinstein had not been charged with assaulting her, said on Thursday that she had no regrets.

“I am still proud that I testified and confronted that convicted rapist,” Ms. Dunning said in a statement, adding: “I am a stronger person for having done so, and I know that other women found strength and courage because I and other Weinstein survivors confronted him publicly.”

“The culture has changed,” she added, “and I am confident that there is no going back.”

In 2022, after a vigorous debate by the justices, a lower appeals court upheld Mr. Weinstein’s conviction. They wrote that the testimony from the additional witnesses had been instrumental in showing that the producer did not see his victims as “romantic partners or friends,” but that “his goal at all times was to position the women in such a way that he could have sex with them, and that whether the women consented or not was irrelevant to him.”

In a quietly dramatic twist, this February, when New York’s highest court heard the producer’s latest and final appeal, four of the seven judges were women, and Thursday’s majority ruling included three female judges.

Their decision landed with stinging dissents. “Fundamental misunderstandings of sexual violence perpetrated by men known to, and with significant power over, the women they victimize are on full display in the majority’s opinion,” Judge Madeline Singas wrote.

The decision to overturn promised to launch fresh debate about the ground rules for criminal convictions in sexual misconduct cases.

“The #MeToo movement showed how important it is to have accounts from multiple accusers,” said Deborah Tuerkheimer, a former Manhattan prosecutor who is now a professor at the Northwestern University Pritzker School of Law. But witness rules — which are strict for a reason — can transform courtrooms into an “alternate universe in which evidence relevant to sex crimes is often kept from the jury.”

“There’s a tension at the heart of it,” she said, “and prosecution in the #MeToo era will continue to deal with this dilemma.”