The Due Process Revolution was the process, carried out mostly by the Supreme Court under Chief Justice Earl Warren, of providing more due process rights to criminal defendants and others.
The Due Process Revolution involved, among other things the "selective incorporation" of the Bill of Rights. This process required the states to adhere to the Bill of Rights even as the federal government did. The Due Process Revolution also added to the idea of what due process was. It added, for example, the idea that people who were arrested had to be read their rights (Miranda v. Arizona) before they could be interrogated.
The Due Process Revolution, then, was a process of expanding the due process protections enjoyed by American citizens.
The "due process revolution" was a direct response by the U.S. Supreme Court under the leadership of Chief Justice Earl Warren to a growing history of state supreme court decisions that were interpreted by Warren and others on the Court as unfairly and unconstitutionally depriving criminal defendants of their rights. The United States, of course, was comprised of the 48 contiguous states, with Alaska and Hawaii being added in 1959. Among those 50 states were 50 different judicial systems, making the propensity for judicial actions in contravention of the intent of the Framers of the U.S. Constitution inevitable, especially given the fractious nature the nation's divide along the old Mason-Dixon line. As a result, state courts were frequently deciding in favor of state prosecutors in instances where the U.S. Supreme Court would later determine defendants' rights had been violated. Among those cases was the U.S. Supreme Court's 1965 decision in Pointer v. Texas, where the defendant, Bob Granville Pointer, stood accused and was tried on a charge of robbery despite the main witness's having left the state. That witness, however, had earlier provided a statement that was used by the prosecution to convict Pointer, who had been without counsel during the earlier crucial phases of the judicial process. In its eventual decision, the U.S. Supreme Court ruled in Pointer's favor, noting that he had been denied due process under the Constitution.
Additional cases involving questionable adherence to the text and, often the intent, of the Constitution precipitated a marked movement by Chief Justice Warren to emphasize individual rights, a movement that became known as the "due process revolution." At the heart of this "revolution" was the Warren Court's efforts at reaffirming the importance of the Fourth and Fifth Amendments to the Constitution that, respectively, protected citizens' rights against unreasonable searches of their property and against self-incrimination.