Professor Thomas is a graduate of the University of Western of Australia. she received her MBBS in 1984, and then trained in Perth as a rheumatologist. She commenced a research fellowship with Peter Lipsky at Southwestern Medical Center, University of Texas in 1990, where she first identified and characterised human circulating dendritic cell precursors. She is now Professor of Rheumatology at University of Queensland, Translational Research Institute and fellow of the Australian Academy of Health and Medical Sciences.
Her research is focused on the study of autoimmune disease and restoration of tolerance. Through this work, she developed and tested the first rheumatoid arthritis vaccine. She has also contributed major insights into the pathogenesis of spondyloarthropathy and autoimmune diabetes, leading to the development of disease biomarkers and therapeutic strategies. Ranjeny is founder and a director of the spin-off company, Dendright, which is developing vaccines to suppress autoimmune diseases.