E. Barrett Prettyman, Jr., a life-long resident of the Washington, D.C. area, received his undergraduate degree from Yale University in 1949. He attended law school at the University of Virginia and served on the editorial board of the Virginia Law Review. In addition he was active in the Student Legal Forum on behalf of which he extended speaking invitations to Justices Robert H. Jackson and Felix Frankfurter, both of whom accepted. In late 1952 Prettyman was selected to clerk for Justice Jackson after graduation the following June.

The Supreme Court was deeply involved in consideration of Brown v. Board of Educationwhen Prettyman began his clerkship. In his history of Browntitled Simple Justice(New York: Alfred Knopf, 1975), Richard Kluger describes in detail the work of the justices in early 1954. "[Chief Justice Earl] Warren's highest hope, for a single unanimous opinion, did not look especially bright. It rested in large part on his overcoming the philosophical reservations of both Felix Frankfurter and Robert Jackson, men who could talk, write and think rings around the Chief Justice. Neither was likely to curl up at Warren's mere bidding."(683)

Justice Frankfurter circulated a memorandum outlining his thoughts in January, and in February Justice Jackson wrote out his ideas in a lengthy draft opinion. He began: "The race problem would be quickly solved if some way could be found to make us all live up to our hypocrisies." Jackson discussed the history of racism from the legislative and judicial perspective and found no acceptable justification for revising the pattern. He finally concluded that segregation should be forcefully put to rest simply because the black population, not the Constitution, had changed.

Barrett Prettyman read Jackson's memorandum and wrote a thoughtful reply. Of Prettyman's work, Kluger wrote: "It is doubtful if any of the many excellent young men who have come fresh out of the law schools or soon thereafter to serve the Justices of the Supreme Court ever served more faithfully or usefully than Barrett Prettyman served Justice Jackson. What part Prettyman's memo played will never be known, but it is a fact that Jackson, having written this much on the segregation cases, wrote no more."(691)

Justice Jackson had a heart attack about seven weeks before the decision in Brownwas handed down in the spring of 1954. During his subsequent extended hospitalization, Prettyman brought work for him to review, including Chief Justice Warren's draft opinion in Brownand Justice Frankfurter's colorful and verbose reports of the justices' conferences. Despite his poor health, Jackson was on the bench on May 17 when the unanimous Browndecision was handed down.

During the summer of 1954 Chief Justice Warren appointed six clerks to study and report ways that desegregation might be implemented. Prettyman, a member of this team, was assigned to map out Spartanburg, South Carolina, in terms of its black and white population and to suggest a prototypical plan for integrating its schools; other clerks were given similar assignments. They then pooled their ideas to formulate an approach the Supreme Court should take on implementation of integration, but could not agree on the important question of timing. Prettyman favored a compromise between forcing immediate desegregation and allowing communities an indefinite period of time to act.

Justice Jackson died in the fall of 1954, and Prettyman went to work for Justice Frankfurter, who had the highest praise for the young man's work and clearly took a personal interest in him. John Marshall Harlan, a judge on the U.S. Court of Appeals for the Second Circuit, was nominated in November 1954 to take Jackson's place on the Court. Harlan's mere name put Senate conservatives on guard because his grandfather had been the sole dissenter in Plessy v. Ferguson; consequently his nomination was held up in the Senate for four months. In the interim he invited Prettyman to be one of his first two clerks, and Prettyman accepted.

At the conclusion of his clerkship in the early summer of 1955, Barrett Prettyman joined the Washington, D.C. firm of Hogan and Hartson, where he was a partner until his death in 2016.