She acknowledged, for instance, that she could not recall precisely which month, or even year, the assault she described had had taken place. Mr. Weinstein’s lawyers also elicited testimony from one of Ms. Sciorra’s old friends, Paul Feldsher, who said that shortly after the incident Ms. Sciorra had not described it as a rape but as a “crazy thing” she had done with Mr. Weinstein. The defense also called the manager of Ms. Sciorra’s building, who said that Mr. Weinstein would not have been allowed up to her apartment without her permission.

The verdict was a victory for Cyrus R. Vance, Jr., the Manhattan district attorney.

Although the jury acquitted Mr. Weinstein of more charges than he was convicted on, the verdict was a significant accomplishment for Mr. Vance and his office, which took a huge risk in bringing Mr. Weinstein to trial in the first place.

Mr. Vance, a Democrat who has long considered himself an ally of feminists, came under enormous pressure to bring a case against Mr. Weinstein after The New York Times and The New Yorker published bombshell articles in October 2017, that detailed the stories of scores of women who accused Mr. Weinstein of abuse and harassment reaching back to the early 1990s.

Mr. Vance was particularly susceptible to the pressure given his own history with sex-crimes cases.

In April 2015, his prosecutors declined to file charges against Mr. Weinstein after an Italian model, Ambra Battilana Gutierrez, accused him of groping her during a business meeting at his Lower Manhattan office. With the help of detectives, Ms. Battilana Gutierrez later recorded Mr. Weinstein appearing to admit that he had touched her. Prosecutors decided that she was a problematic witness because she had given inconsistent accounts in a separate sexual assault case in Italy.

Four years earlier, Mr. Vance dismissed rape charges against another powerful man, Dominique Strauss-Kahn, the head of the International Monetary Fund at the time, after a hotel maid in Manhattan accused him of rape. Again, Mr. Vance’s office said it had doubts about the woman’s credibility: She had fabricated a story about a gang rape in her native Guinea.

After the verdict on Monday, Mr. Vance told reporters at a news conference, “It’s a new day because Harvey Weinstein has finally been held accountable for crimes he committed.”

The verdict may lead to change in the prosecution of complex sex-crimes cases.

Prosecutors have traditionally been averse to bringing rape cases in which witnesses admit to having sex consensually with their assailants at other times.