Ash was born in Canberra and moved to Sydney with his family at an early age. He completed his secondary schooling at Sydney Grammar School. He completed his Bachelor of Medicine degree at the University of New South Wales and was awarded First Class Honours.
He completed his Basic Physician Training at Westmead Hospital and his Advanced Training in Endocrinology at Royal Prince Alfred (RPA) and Bankstown-Lidcombe Hospitals in Sydney.
He is currently appointed as a Staff Specialist at RPA and Bankstown-Lidcombe Hospitals and as a Visiting Endocrinologist at Norwest Private Hospital and the Chris O'Brien Lifehouse. He is a senior conjoint lecturer with the University of New South Wales and a clinical examiner for the Royal Australasian College of Physicians.
He has a strong interest in treating disorders of the thyroid gland which constitutes a significant proportion of his clinical practice. He contributes to the clinical research of thyroid disorders, in particular thyroid cancer and thyroid dysfunction in pregnancy and infertility. He is an integral part of the multi-disciplinary thyroid cancer team at RPA and works very closely with the Fertility Unit at RPA. He has established the Thyroid Pregnancy Clinic at RPA and the multidisciplinary High Risk Diabetes Foot Service at Bankstown-Lidcombe Hospital, where he is the medical lead. He is involved in supervising and training Endocrinology advanced trainees, junior medical staff and medical students from the Universities of Sydney and New South Wales.
He is professionally affiliated with the Royal Australasian College of Physicians, the US Endocrine Society, the Endocrine Society of Australia and the American Thyroid Association. He regularly attends national and international scientific meetings. He has published and reviewed articles in a number of peer reviewed clinical journals.