During his career at the Bar John Chadwick had a heavy litigation practice which included banking, insurance, insolvency and commercial fraud. He was standing Counsel to the DTI and sat as a Judge of the Courts of Appeal of Jersey and Guernsey. Appointed in 1991 at the age of 50 as a High Court Judge, he sat in the Chancery Division for 6 years. He was elevated to the Court of Appeal in 1997, where he dealt with civil appeals from the Commercial Court and Chancery Division. He retired from that court in November 2007.
In January 2008, Sir John was appointed a Lieutenant Bailiff of the Royal Court of Guernsey. He sat as Deputy Chief Justice of the Dubai International Financial Centre Court, and as President of the Court of Appeal of The Cayman Islands until 2016.