The Hughes Court ruled 6–2 (Justice Benjamin Cardozo did not participate) in Johnson v. Zerbst (1938) that federal criminal defendants have a Sixth Amendment right to the assistance of counsel. The case involved John A. Johnson, who was convicted for passing off counterfeit $20 bills. He was tried and sentenced in federal court in South Carolina to four years without the benefit of an attorney. In a habeas corpus (a later, collateral challenge to an original conviction) proceeding, Johnson (with the benefit of counsel) argued that his conviction should be set aside because he was not afforded an attorney.

Writing for the Court, Justice Hugo Black agreed that the “Sixth Amendment withholds from federal courts, in all criminal proceedings, the power and authority to deprive an accused of his life or liberty unless he has or waives the assistance of counsel.” The Court emphasized the importance of counsel and that even intelligent lay persons do not sufficiently know the law to be able to defend themselves adequately. Black also ruled that Johnson did not knowingly waive his right to an attorney.