Dr Mary Gleeson is a Consultant Haematologist at Guy's and St Thomas' NHS Foundation Trust, with a specialist interest in lymphoma, clinical research, and lymph node diagnostics. After completing specialist training in haematology, Dr Gleeson undertook a clinical research fellowship at The Royal Marsden, focusing on UK NCRI national clinical trials in diffuse large B-cell lymphoma and peripheral T-cell lymphoma. During this time, they obtained a Doctorate in Medical Research (MD Res) from the University of London.

Dr Gleeson is a member of the Royal College of Physicians of Ireland, the Royal College of Pathologists (UK), and the European Haematology Association. They currently serve as the Research and Development Lead for Haematology at Guy's Hospital and act as Principal Investigator for lymphoma clinical trials at Guy's Hospital and early-phase trials at the Sarah Cannon Research Institute in London.

An active contributor to the UK NCRI Lymphoma High-Grade Subgroup and the T-cell Lymphoma Working Group, Dr Gleeson has presented research at major international conferences including ASH, EHA, and ICML (Lugano). Their work has been published in leading peer-reviewed journals such as The Lancet, The Lancet Haematology, Blood, Annals of Oncology, and The British Journal of Haematology.