The case involved a California man who killed his ex-girlfriend after she complained to police.
The US Supreme Court has strengthened the constitutional right to confront one's accusers in court.
In a 6-to-3 decision announced on Wednesday, the high court invalidated a judge's exception to a criminal defendant's Sixth Amendment right "to be confronted with the witnesses against him."
The majority justices made the ruling in the case of a California man who killed his ex-girlfriend. Prosecutors allowed the jury to hear about a domestic-abuse complaint the ex-girlfriend had filed with police against the defendant three weeks before he shot and killed her.
Lawyers for the defendant objected, saying since the ex-girlfriend was now dead, there was no way for them to cross-examine her allegations of domestic violence. They urged the Supreme Court to overturn the boyfriend's conviction and order a new trial.
Prosecutors countered that the boyfriend forfeited his right to confront his ex-girlfriend in court when he killed her.
The majority justices disagreed. Writing for the court, Justice Antonin Scalia said allowing testimony by police about the murder victim's earlier domestic violence allegations violated the defendant's Sixth Amendment right to confront witnesses against him.
"We decline to approve an exception to the confrontation clause unheard of at the time of the founding or for 200 years thereafter," Justice Scalia wrote.
He said that prior to 1985 American courts never invoked the concept that a defendant might forfeit his or her right to confront witnesses other than in cases involving deliberate witness tampering.
The decision, in a case called Giles v. California, is important because it bolsters a 2004 landmark Supreme Court opinion written by Scalia enforcing the right to face one's accusers in court. It establishes a demanding test for when certain out-of-court statements may be introduced as evidence in a trial.