Its 7-to-2 ruling Wednesday reverses a Louisiana death-penalty conviction.
The US Supreme Court has put an exclamation point on a 1986 precedent that bars racial discrimination in jury selection.
The justices did it in a 7-to-2 ruling announced on Wednesday, reversing the capital-murder conviction of a black Louisiana death-row inmate.
Allen Snyder won the right to a new trial because the prosecutor in his 1996 murder case improperly excluded at least one African-American from the jury.
The case has been closely followed after reports that the state prosecutor, James Williams, excluded all five prospective African-American jurors from serving on the panel and then compared the defendant to O.J. Simpson during closing arguments. Analysts said it was an attempt to enrage the all-white jury and provoke a death sentence for a black defendant.
Writing the majority opinion, Justice Samuel Alito did not mention the O.J. Simpson episode. Instead, he focused on the plight of one prospective black juror, Jeffrey Brooks, who was excluded from the panel.
Justice Alito said the prosecutor told the trial judge that he'd excluded Mr. Brooks from the jury because he looked nervous and because as a student-teacher with only one semester until college graduation he might feel an urgency to rush through jury deliberations to get back to school.
The trial judge accepted the explanations and brushed aside allegations by Snyder's lawyer that race was playing an illegal role in the trial.
On Wednesday, the Supreme Court said that action by the trial judge was a "clear error."
Alito said the first justification for excluding Brooks does not appear to have been relied on by the trial judge. But he added that the second justification was "suspicious." Alito writes: "The prosecutor's proffer of this pretextual explanation naturally gives rise to an inference of discriminatory intent."