Tree mortality in many eucalypt-dominated forest ecosystems in Australia is thought to be associated with climatic extremes, and climate-driven shifts in pest and pathogen dynamics. Climatic factors are likely to predispose marri (C. calophylla) to the canker disease (fungal pathogen – Q. coyrecup), causing marri decline in Western Australia. In this study, we empirically examined the effects of drought on canker disease predisposition, and the interactions between drought stress, the pathogen and the plant physiological and biochemical (defence) response, which is yet to be investigated in any single plant pathosystem. We conducted an experiment with well-watered and drought-stressed treatments, each with inoculated and non-inoculated plants. Moreover, drought stress was applied either before inoculation, after inoculation, or throughout the experiment. Canker lesions developed in all inoculated treatments irrespective of the watering regime. However, the rate of canker growth in well-watered plants was greater in the plants that had experienced drought stress before inoculation. Photosynthesis and growth were significantly reduced due to the disease in well-watered treatments but not in drought-stressed treatments. These effects could be attributed to the reductions in stem hydraulic conductivity and stomatal conductance, rather than biochemical limitations to photosynthetic capacity. Data on secondary metabolites, potentially involved in plant biochemical defence, will also be presented for the different treatments.