It was not until 1932, in Powell v. Alabama, that the Supreme Court reversed the convictions of eight capital cases because the defendants had not been appointed proper counsel for their defense. The Court decided that “in a capital case, where the defendant is unable to employ counsel, and is incapable adequately of making his own defense because of ignorance, feeble mindedness, illiteracy, or the like, it is the duty of the court, whether requested or not, to assign counsel for him as a necessary requisite of due process of law.” The Court decided this case on 14th Amendment due process grounds, however, not based on the 6th Amendment.
In Johnson v. Zerbst (1938), the Court held that the 6th Amendment required that all defendants who could not afford lawyers be offered court-appointed ones. But this case applied only to federal courts. Indeed, a 1942 case, Betts v. Brady, explicitly denied this constitutional guarantee to state courts.
In 1963, the Court, in Gideon v. Wainwright, incorporated this newer understanding of the 6th Amendment’s right to “have the assistance of counsel” into the 14th Amendment, so that it henceforth applied to the states. Gideon essentially adopted the standard of Zerbst, that courts may not “deprive an accused of his life or liberty unless he has or waives the assistance of counsel.” Gideon applied only to felonies, however; a 1973 decision, Argersinger v. Hamlin, recognized the right to counsel even in misdemeanor trials. And in a pair of cases decided in 2012 (Missouri v. Frye and Lafler v. Cooper) the Court upheld the 6th Amendment right to counsel during plea bargaining. Justice Kennedy, noting “the reality that criminal justice today is for the most part a system of pleas, not a system of trials,” determined that the 6th Amendment must adapt to that new reality.
Starting with Gideon, the Supreme Court’s interpretations of the 6th Amendment has turned the ancient restriction on a right to counsel on its head. The earliest English practice was to deny counsel in all but misdemeanor trials. Now, defendants in all criminal trials have a right to counsel except for the most petty offenses. This right is in force unless and until the defendant explicitly waives it. In fact, the Court has even held that the 6th Amendment protects its opposite: it guarantees to a defendant the right to represent himself [Faretta v. California (1975)]. And even this right to defend oneself may be denied if the court determines that the defendant is not competent to make that choice.