WASHINGTON — In an unusual rebuke from a former member of the Supreme Court, Justice John Paul Stevens said on Thursday that Judge Brett M. Kavanaugh was not qualified to sit on the court.

Justice Stevens said he came to the conclusion reluctantly, changing his mind about Judge Kavanaugh’s nomination after the second round of the judge’s confirmation hearings last week. Judge Kavanaugh’s statements at those hearings, Justice Stevens said, revealed prejudices that would make it impossible for him to do the court’s work, a point he said had been made by prominent commentators.

“They suggest that he has demonstrated a potential bias involving enough potential litigants before the court that he would not be able to perform his full responsibilities,” Justice Stevens said in remarks to retirees in Boca Raton, Fla. “And I think there is merit in that criticism and that the senators should really pay attention to it.”

“For the good of the court,” he said, “it’s not healthy to get a new justice that can only do a part-time job.”