The Metropolitan Opera fired the conductor James Levine on Monday evening, ending its association with a man who defined the company for more than four decades after an investigation found what the Met called credible evidence that Mr. Levine had engaged in “sexually abusive and harassing conduct.”

The investigation, which the Met opened in December after a report in The New York Times, found evidence of abuse and harassment “both before and during the period” when Mr. Levine worked at the Met, the company said in a statement.

It was an extraordinary fall from grace for a legendary maestro, whom many consider the greatest American conductor since Leonard Bernstein.

[With James Levine Fired, Should We Rethink Maestro Worship]

The Met did not release the specific findings of its investigation, which it said had included interviews with 70 people. But the statement said that the investigation had “uncovered credible evidence that Mr. Levine engaged in sexually abusive and harassing conduct toward vulnerable artists in the early stages of their careers, over whom Mr. Levine had authority.” It said that it was terminating its relationship with Mr. Levine, who is currently the company’s music director emeritus and the artistic director of its young artists program.