Worthen attended the J. Reuben Clark Law School at BYU. He became a member of an honor society called the Order of the Coif. In 1982, he again graduated with the highest honors ("summa cum laude") and the best grades in his class. Then he worked as a law clerk (a lawyer who helps a judge make legal decisions) for Judge Malcolm R. Wilkey on the U.S. Court of Appeals for the D.C. Circuit. He also worked as a law clerk for Associate Supreme Court Justice Byron R. White. From 1984 to 1987, Worthen worked as a lawyer in Phoenix, Arizona, for a law firm called Jennings, Strouss & Salmon. Worthen found that he was very interested in the history of laws, so he decided that he wanted to teach law.