Mary Laffey specializes in pediatric critical care and neonatal/pediatric transport medicine. She provides intensive care and sedation services.

Her research interests include the development of a pediatric post-cardiac arrest hypothermia protocol, and the development of a pediatric intensive care unit status asthmaticus order set.

She serves as a nurse practitioner in the Department of Pediatrics, Division of Pediatric Critical Care, at Saint Louis University School of Medicine.

Laffey is a member of the Society of Critical Care Medicine. She is an instructor for Pediatric Fundamental Critical Care Support (PFCCS), a course designed for those who treat children with critical care needs, such as in an emergency room or intensive care unit. It is an accredited course for health care professionals. She is also an instructor for Patient Airlift Services (PALS).

Laffey put her medical expertise to good use in Haiti, where she was part of a mission trip, post-earthquake.