In Johnson v. Louisiana, the U.S. Supreme Court examined whether a state law allowing for less than unanimous jury verdicts in criminal cases violated the Sixth and Fourteenth Amendments of the Constitution. The case involved Gary Duncan, who was convicted by a 9-3 jury vote in Louisiana on charges of simple battery - an offense punishable by imprisonment under state law. Duncan challenged his conviction arguing that it violated his constitutional right to trial by jury because of the non-unanimous decision. The Supreme Court ruled 5-4 against Duncan, upholding Louisiana's law permitting convictions based on less-than-unanimous juries in certain circumstances. The majority opinion held that while unanimity is required for federal trials under the Sixth Amendment, this requirement does not extend to state trials via incorporation through Fourteenth Amendment due process clause or equal protection clause. This ruling stood until April 2020 when another case from Louisiana (Ramos v. Louisiana) led to a reversal; now all states are required to have unanimous juries for serious crimes.

The dissenting opinion in Johnson v. Louisiana argued that the majority's decision to uphold non-unanimous jury verdicts in criminal cases was a departure from the traditional understanding of reasonable doubt and could potentially undermine public confidence in the justice system. The dissenters believed that allowing convictions based on less than unanimous agreement among jurors would dilute the standard of proof beyond a reasonable doubt, which is fundamental to ensuring fairness and accuracy in criminal trials. They also expressed concern about potential racial bias, noting that non-unanimous juries were originally introduced as part of an effort to marginalize African American jurors during Reconstruction. Furthermore, they pointed out inconsistencies between this ruling and other Supreme Court decisions requiring unanimity for federal juries and for state court juries deciding capital cases.