In theory, a candidate for the Supreme Court in the United States need not have any judicial experience. There are benefits and drawbacks to such a candidate.
The Supreme Court decides a handful of cases every year and turns away most appeals to its authority. As the final authority on what the U.S. Constitution means, many of its decisions make new law and are not based upon established precedent. All of the inferior courts, federal and state, are bound by precedent when making decisions.
A non-judge will not be in the habit of relying on existing precedent when considering a case. He or she will approach each Supreme Court case with a slightly different perspective than appointees with judicial experience.
A President appoints individuals to the Supreme Court for many reasons. Often, the legal background and political temperament that the candidate represents is more important than any prior experience. Earl Warren came to the Court after three terms as Governor of California. With a reputation as a crime fighting district attorney, and as the only U.S. governor ever elected unopposed, Warren was chosen to represent Republican ideals in the chamber.
41 of the over 110 Justices of the Supreme Court have had no prior judicial experience. All have been lawyers, however. The Justice credited with establishing the role of the Court in the early days of the Republic, John Marshall, had never been a judge.
The Supreme Court is asked to review thousands of cases each year. The members choose cases with substantive questions of Constitution or law. Judicial experience allows them experience in determining the existence of these factors as a case is considered.
Non-judges may not recognize that not every case is deserving of review by the Supreme Court. Lawyers often speak about fighting a case “all the way to the Supreme Court”. The reality is that the Court agrees with decisions made lower courts in most cases and will not hear those cases.
Robert Bork and Harriet Miers are two recent nominees that failed to receive Senate approval of their appointments to the Supreme Court. Bork was seen as outside the mainstream of politics and judicial thought by many Senators, as a rock-ribbed conservative. Miers, despite a long history as a lawyer, was deemed unprepared for a top judicial post by many and withdrew her nomination.
The latest Justice to be confirmed is Elena Kagan. She had no experience as a judge, and is the only such of the current nine serving Justices.