Dr. Heslop's initial faculty appointment was as Assistant Member of the Division of Bone Marrow Transplantation in the Department of Hematology-Oncology at the St. Jude Children's Research Hospital, in Memphis in 1991. She was promoted to Associate Member in 1994. She also held an appointment as Associate Professor in the Department of Pediatrics at the University of Tennessee in Memphis. Dr. Heslop received her current appointments at the Baylor College of Medicine in Houston, Texas in 1997. She was named as the first Dan L. Duncan Chair for Baylor College of Medicine in 2006.

Dr. Heslop's research centers on adoptive immunotherapy with gene-modified effector cells to improve hemopoietic stem cell transplantation and cancer therapy. She currently directs a Lymphoma SPORE program and a program project grant from the NCI, as well as a Specialized Center of Research from the Leukemia and Lymphoma Society. Her research focus is to develop safe and effective T-cell immunotherapies for lymphoma and other Epstein-Barr virus-associated malignancies, including Hodgkin's Disease and nasopharyngeal cancer. Dr. Heslop also runs studies using third party CTLs to treat viral infections after transplant.