Fire from volcanic activity (FFVA) is a highly dangerous and largely understudied hazard arising from volcanic activity. FFVA can be caused by a variety of volcanic hazards and can greatly compound the damage and losses associated with volcanic activity, in addition to creating complications for event response and mitigation. In this study, we develop a FFVA ignition probability model underpinned by a widely applicable fault tree, which identifies the mechanisms that can lead to fire ignition from volcanic activity. By assigning values to each node of the fault tree, our model can be used to consider the relative probabilities associated with different fire ignition mechanisms. We couple this model with a fire spread model to evaluate hazardous areas and associated impacts caused by FFVA. To demonstrate the applicability of our model, we use an eruption scenario for volcanic ballistic projectiles (VBPs) in the Auckland Volcanic Field (Aotearoa New Zealand). We found that burn zones were highly sensitive to wind conditions and fuel availability. The maximum credible damaging wind permutation for VBP-ignited FFVA in Auckland results in over NZ$3.9 billion damage to buildings and infrastructure, four times greater than if fire spread was not considered. This case study demonstrates the potential for FFVA to compound and greatly increase the impacts caused by other volcanic hazards and we suggest that more study is needed to better understand, evaluate and plan for FFVA.