Dr. Mustard has had a diverse and esteemed career in the health sciences, medical research, research in the natural and social sciences, and the private sector. After earning his MD from the University of Toronto, and Ph.D. from the University of Cambridge, Dr. Mustard joined the medical faculty at the University of Toronto. During his tenure at the University of Toronto and McMaster University, he developed a major research career in platelets, thrombosis and cardiovascular disease.

In 1982, Dr. Mustard took on the task of creating and establishing a unique Canadian institution, The Canadian Institute for Advanced Research. Dr. Mustard has been a champion in Canada of interdisciplinary research including the socioeconomic determinants of human development and health. He co-chaired a report for the Government of Ontario on early child development with specific community recommendations (The Early Years Study).

In 2004 Dr. Mustard founded The Council for Early Child Development. As part of this critically important initiative, Dr. Mustard and his colleagues have emphasized to all sectors of society the crucial nature of early human development in fostering healthy populations and optimizing well-being. Dr. Mustard is a Companion of the Order of Canada. The University of Calgary honoured Dr. Mustard with a named chair in the UofC Faculty of Medicine.