He was appointed to the Alpha Omega Alpha Honour Medical Society in 1957 and received his M.D. degree (Magna Cum Laude) from The University of Toronto in 1958. He subsequently did Post Graduate Training Internal Medicine with a subspeciality interest in Endocrinology and obtained an F.R.C.P.(C.) degree in 1963. He then received an R. Samuel McLaughlin Travelling Fellowship to the Thyroid Unit of the Massachusetts General Hospital from 1963-1964. Subsequently, he was appointed a Scholar, Medical Research Council of Canada (1964-1969).

Since 1964, he has been an Academic Full-Time Physician-Scientist in the Department of Medicine, University of Toronto at Mount Sinai Hospital and has directed the Thyroid Research Lab/Gene Expression Laboratory as a Senior Scientist within the Samuel Lunenfeld Research Institute of Mount Sinai Hospital. Dr. Walfish has also served as the Director of Endocrine Division within the Department of Medicine at Mount Sinai Hospital, Toronto from 1971 to 1989 and was promoted to the rank of Full-Professor of Medicine in 1982 and Honorary Full-Professor of Paediatrics in 1983, Otolaryngology in 1996 and Pathology & Laboratory Medicine in 2007.

His research laboratory has made numerous contributions to the study of thyroid disease which have led to the improved management of several thyroid disorders at both a national and international level (over 160 peer-reviewed publications) to include the early detection and treatment of congenital hypothyroidism in newborn infants and the prevention of its mental retardation sequelae, the application of ultrasound and needle aspiration biopsy in the detection and management of thyroid nodules with cancer, the detection of post-partum thyroiditis and its thyroid dysfunctional consequences. He continues to perform both clinical and basic science research to improve our understanding of many aspects of thyroid physiology and pathology. Since 1988, he has performed studies on the molecular mechanisms of gene activation of thyroid hormone, which have been published in prestigious peer-reviewed journals. He has also continued clinical and basic science studies applied to the management of thyroid cancer.

In 1983, he received an Award of Merit from the City of Toronto for his contributions in establishing newborn screening for congenital hypothyroidism in Metropolitan Toronto and the province of Ontario. Dr. Walfish has been honoured by election to Fellowship in The Royal Society of Medicine of England, Endocrinology Section in 1986, appointed a Member of the Order of Canada in 1990, and awarded the 125th Anniversary of Canadian Confederation Commemorative Medal in 1992. In 1995, he received an Ambassador Award from The Metropolitan Toronto Convention and Visitors Association and a special citation from the American Thyroid Association for his activities as Chairman of the Local Organizing Committee for the 11th International Thyroid Congress held September 1995 in Toronto, Canada. In 1998, he was selected as the first recipient of the Council Award from the College of Physicians and Surgeons of Toronto honouring his contributions in thyroidology which have had a significant impact on healthcare delivery in Ontario and world-wide. He also received a 2001 Jonas Salk Prize co-sponsored by the Ontario March of Dimes and Aventis-Pasteur for the elimination of newborn cretinism in Ontario and throughout the world as well as a 50th Anniversary Jubilee Medal on the Reign of Queen Elizabeth II in 2002. For outstanding contributions in clinical thyroidology, he was honoured in 2004 as the first Canadian to receive the Paul Starr Award from the American Thyroid Association. In 2007, he was awarded the Canadian Medical Association Medal of Service and the American Thyroid Association Sidney H. Ingbar Distinguished Lectureship Award. In 2008, he was honoured by an appointment to the Order of Ontario.

In 2009 Dr. Walfish was honoured with a third award from the American Thyroid Association by receiving the John B. Stanbury Medal in Thyroid Pathophysiology for his research contributions which has impacted on patient care and he was elected to Fellowship in the Canadian Academy of Health Sciences for outstanding career contributions to the advancement of health care in Canada and abroad.