Has trained clinically and in research in Sydney, Newcastle and Melbourne and was appointed inaugural Professor of Geriatric Medicine at the University of Western Australia in 1998. He established a productive research unit aimed at translational issues focusing on the health needs of older people culminating in 2006 the creation of the Western Australian Centre for Health and Ageing at the University of Western Australia. Leon remains a practicing geriatrician at Royal Perth Hospital. Leon has served on numerous government committees addressing the health needs of older people. He is a Past President of the Australian and New Zealand Society for Geriatric Medicine. He has published over 460 peer-reviewed articles addressing a wide variety of health issues in older people.

Leon was the inaugural AAG Glenda Powell Travelling Fellow and immediate AAG Board Nominee.

In 2017 Leon was awarded Officer of the Order of Australia for his work in geriatric medicine and with people with dementia.