Following WWII, Prentice became a member of the Council of
Papua New Guinea Affairs, responsible for the promotion of legal education for Papua New Guineans. He was influential in the establishment of the Faculty of Law at the
University of Papua New Guinea. In 1970 Prentice was appointed a Justice of the Supreme Court of Papua New Guinea and served on that court for 10 years. He was appointed successively senior puisne judge in 1975 and chief justice in 1978. His period on the bench transected the momentous years of change through self-government, independence and post-independence. Prentice was responsible for many leading judgments, particularly in the area of constitutional interpretation, which have had a profound effect on the development of the
law in Papua New Guinea. In 1978 Prentice presided over a traffic accident case in which Morrie Modeda - accused of a dangerous driving charge, occasion a man's death - was hacked to death by relatives of the deceased as he and court party including Prentice attended an inspection at the site of the accident. In the concluding proceedings Prentice termed the action "cold-blooded, planned treachery" and described it as a "lawless and disgraceful episode". In March 1980, Sir William Prentice resigned as Chief Justice in controversial circumstances relating to the
Rooney crisis - a constitutional crisis that tested the principle of the separation of powers. Prentice and four other judges resigned over the affair. He returned to Australia where he served for some years as a senior member of the
Administrative Appeals Tribunal. He retired from active practice in 1987. ==Personal==