Moore was elected to the Colorado Supreme Court in 1948. He served from 1949 until 1968 on the bench. During his twenty years with the Court, Moore was involved in more than 5,000 decisions and wrote 1,038 opinions. He said of his time as a justice, "I particularly remember my dissents. I really relished them; they had more conviction. I may be wrong, but I'm never in doubt." He served three terms as Chief Justice (1957, 1967 and 1968). In 1969, Moore retired from the Colorado Supreme Court. During his service, he wrote the majority opinion in 1968 that set a still-standing precedent that it is unconstitutional to require a defendant to prove insanity. He stated that it was the prosecution's burden to prove guilt or sanity: "It cannot be done … for the very simple reason that in this state our concept of due process of law prohibits it."
