Ash completed a PhD (2002) in Salmonella pathogenesis with Prof Gordon Dougan at Imperial College. He conducted a first post-doc with Dr. Greg Bancroft at the London School of Hygiene & Tropical Medicine, focussing on T cell immunity to the gram-negative bacterium, Burkholderia pseudomallei (the agent of melioidosis). In 2006, he moved to Brisbane to work with Prof Christian Engwerda at QIMR. He focussed on experimental models of T cell immunity to protozoan parasites. With NHMRC CDF and Project funding in 2012, he starting his independent research group, and became a full Group Leader and Co-ordinator of the Infectious Diseases Program at QIMR Berghofer. In 2020, he was recruited to the Department of Microbiology and Immunology, University of Melbourne, where he currently leads the Department's efforts in single-cell genomic analysis of immune cells.