Understanding future climatic change impacts on ecosystems requires long-term models assessing species responses. The invasive house mouse (Mus musculus) responds to fire and climatic fluctuations, potentially contributing to ecosystem disruptions. While house mice are globally distributed, research in Australia has primarily focused on agricultural and arid environments, with little attention to natural temperate ecosystems. We investigated house mouse dynamics in Gariwerd (Grampians National Park) using a long-term dataset spanning highly variable climatic conditions. We conducted annual small mammal trapping at 36 monitoring sites between 2008 and 2022, a period marked by wildfires, droughts, and flooding. Generalised Additive Mixed Models (GAMMs) assessed the impact of fire, rainfall, competition, vegetation composition, and productivity on house mouse abundance. Across 131,040 trap nights, we recorded 1956 house mouse captures. Our analysis revealed that fire, rainfall, and competition drove population dynamics, with mouse abundance peaking after fire and during elevated short-term rainfall and declining with high long-term rainfall and increased native small mammal abundance. Climate change-induced increases in drought and wildfire may enable house mouse population expansion in temperate ecosystems, potentially amplifying invasive predator densities and threatening native mammal populations. Our research advances a state-and-transition model that describes the dynamics of house mouse populations under climatic extremes, emphasizing the complex interplay of fire, climate variability, and interspecific competition. This model describes how temperate ecosystems will respond to climate-driven disturbances such as fires and droughts and provides a conceptual framework for the development of more targeted, adaptive strategies for mitigating the impacts of invasive species and ecosystem shifts in the face of climate change.