Dr. Cunniff is currently Chief of the Division of Medical Genetics and a Professor of Pediatrics at Weill Cornell Medical College. He is a member of the American College of Medical Genetics and Genomics and the American Society of Human Genetics. He served on the Board of Directors and as President of the American Board of Medical Genetics, Board of Directors and Secretary of the American College of Medical Genetics and Genomics, Chairperson of the Committee on Genetics of the American Academy of Pediatrics, and as a member of the National Conference and Exhibition Planning Group of the American Academy of Pediatrics. He was a member of the Center for Disease Control and Prevention's National Task Force on Fetal Alcohol Syndrome and Fetal Alcohol Effect and the Care Considerations Expert Panel for Duchenne Muscular Dystrophy. He is currently on the editorial board for Molecular Syndromology. Dr. Cunniff is a clinically active pediatric geneticist who is board certified in pediatrics and clinical genetics.

Dr. Cunniff's research has focused on population based surveillance for genetic disorders and developmental disabilities including Duchenne and Becker muscular dystrophy, Fetal Alcohol syndrome, autism spectrum disorders and developmental disabilities. He has also published extensively on birth defect syndromes, disorders of sexual development and the contribution of birth defects to mortality in hospitalized patients. He currently serves as Registrar for the Bloom's Syndrome Registry, which maintains patient samples and clinical information on persons with Bloom's Syndrome.

Dr. Cunniff has taught genetics at all levels of medical and postgraduate medical training. He directed basic science genetics courses at the University of Arkansas for Medical Sciences and at the University of Arizona College of Medicine. At the University of Arizona College of Medicine he was on the Dean's List for Outstanding Basic Science Education and was a member of the Academy of Medical Education Scholars. At Weill Cornell Medical College he is currently the Unit Leader for the Genetics Unit of Essential Principles of Medicine. He has been Program Director of the Medical Genetics Residency at the University of Arizona College of Medicine. He lectures regularly for educational programs of the American Academy of Pediatrics.