In 1967, Chrétien opened a laboratory on polypeptide hormones at the Clinical Research Institute of Montreal (CRIM), where he would remain until 1999.[4] His research proposed that peptide hormones are produced from large precursor proteins. He was an Associate Member, Experimental Medicine at McGill University from 1969 to 1999. In 1999 he was scientific director and CEO of the Loeb Health Research Institute at the Ottawa Civic Hospital.[5]
Chrétien was a Professor of Medicine in the Faculty of Medicine at the Université de Montréal from 1975 to 1999. He was Chief of Endocrinology at Hôtel-Dieu de Montréal. In 1998, he was appointed a Professor, Department of Medicine, Faculty of Medicine, University of Ottawa. In 2006, he was appointed Senior Scientist of Hormone, Growth and Development at the Ottawa Health Research Institute.[3]