I have been a federal court of appeals judge since 1981, and before that I had been a full-time law professor since 1968. And since becoming a judge I have continued to teach part time and do academic research and writing. The United States is unusual if not quite unique in the porousness of the membranes that separate the different branches of the legal profession. The judiciary both federal and state is a lateral-entry institution rather than a conventional civil service; and unlike the British system (though that system is loosening up and becoming more like the U.S. system), in which the judges are drawn from a narrow, homogeneous slice of the legal profession--namely, senior barristers--American judges are drawn from all the different branches of the profession, including the academic. Among appellate judges who came to the bench from academia are Oliver Wendell Holmes (although he had joined the Harvard Law School faculty only months before being appointed to the Supreme Judicial Court of Massachusetts, he had been doing academic writing for many years), Harlan Fiske Stone, William O. Douglas, Felix Frankfurter, Antonin Scalia, Ruth Ginsburg, and Stephen Breyer (U.S. Supreme Court); Calvert Magruder, Charles Clark, Jerome Frank, Joseph Sneed, Harry Edwards, Robert Bork, Ralph Winter, Frank Easterbrook, Stephen Williams, J. Harvie Wilkinson, John Noonan, Douglas Ginsburg, S. Jay Plager, Kenneth Ripple, Guido Calabresi, Michael McConnell, William Fletcher, and Diane Wood (U.S. courts of appeals); and Roger Traynor, Hans Linde, Benjamin Kaplan, Robert Braucher, Ellen Peters, and Charles Fried (state supreme courts). (The list is not intended to be exhaustive.) All these are appellate judges but a number of distinguished federal district judges have been appointed from the academy as well, such as Jack Weinstein, Robert Keeton, and Louis Pollak. And these lists are not exhaustive.
