John Greally is a professor of genetics and pediatrics at the Albert Einstein College of Medicine.

A native of Galway, Ireland, Greally received his honours degree in medicine from the National University of Ireland in Galway. He trained in paediatrics at the Children’s Hospital of Pittsburgh and clinical genetics at Yale University. He received his higher degrees in medicine (D.Med.) and science (Ph.D.) from the University of Galway, and has been awarded a Fellowship of the American College of Medical Genetics (FACMG).

Greally has over 210 peer-reviewed publications and is the recipient of numerous National Institutes of Health and other grant awards. His research program is focused on identifying functional non-coding variants in the human genome and using them to understand human heritable disease. He is the Founding Director of the Center for Epigenomics at Einstein.

Greally serves as an attending physician in the Genetics service of Montefiore Medical Center, specialising in dysmorphology and medical genomics. He leads the New York Center for Rare Diseases (NYCRD).

In 2025, Greally was recognized by the Bronx Borough President with a Proclamation for his work in the communities of the Bronx. His book entitled Epigenetics: History, Molecules and Diseases was published in 2025 by Cold Spring Harbor Laboratory Press.