John lived in Highett and attended Highett High School after which he joined the Australian National Line whilst studying Accountancy. He then moved into advertising and marketing and enjoyed a successful career in senior corporate management roles, mainly in import and wholesale with the Brash Group until 1983.

John married his childhood sweetheart Helen in 1969 and they have two children, Sarah and Andrew. Sarah is an interior designer and has two children (Jack and Harry) to her first husband Steve, who tragically died in 2016 when the boys were just 4 and 6 years old. Sarah married her current husband Aaron in 2019. Andrew is a Financial Planner and MD of the family company Hewison Private Wealth. He is married to Joanna who is a dietician, and they have two children, Summer and Oscar.

At the age of 36, John decided to depart corporate life as he was constantly away from home with two young children which was too hard on the family, and he had become tired of corporate politics.

He then formed a consulting business until he encountered the fledgling Financial Planning profession in 1985. He has since obtained a Masters in FP and is a Certified Financial Planner (CFP). He has also built the highly successful independent financial planning business Hewison Private Wealth (HPW) into a company that has six equity partners, 18 Senior and Associate advisers, and employs a total of 45 people.

John is a Life Member and former Chairman of the Financial Planning Association of Australia and a former director of the international Financial Planning Standards Board. He is also a Fellow of the Australian Institute of Company Directors and a Justice of the Peace.

John retired from HPW in 2020 but remains an equity partner and Chairman of the board. The rest of his time is taken up with family, travel, golf (he is a member of Victoria Golf Club), art (painting and drawing with oils and charcoal), boating, fishing, and enjoying the family holiday house at Blairgowrie, scuba diving and is currently writing two books. John is also a joint founder and Life Member of the Gunnamatta Surf Life Saving Club.

John became Treasurer of Probus in 2021.