Climate change and other factors have contributed to an increased frequency and intensity of global wildfires in recent years. Ammonium-based fire retardants are widely used to suppress or delay the spread of fire and have generally been regarded as presenting a low risk of acute toxicity to fauna. However, studies have raised concerns about their potential to cause indirect or sub-lethal effects, and toxicity information regarding the potential for such impacts in aquatic species is limited. To address these knowledge gaps, we used an untargeted metabolomics approach to evaluate the sub-lethal physiological and metabolic responses of striped marsh frog (Limnodynastes peronii) tadpoles exposed to a concentration gradient of the ammonium polyphosphate (APP)-based fire retardant Phos-Chek LC95W (PC). Acute exposure (96 h) to PC significantly altered the relative abundance of 14 metabolites in whole tadpoles. The overall metabolic response pattern was consistent with effects reported for ammonia toxicity and also suggestive of energy dysregulation and osmotic stress associated with alterations to physicochemical water quality parameters in the PC treatments. Results suggest that run-off or accidental application of this formulation into waterways can have significant sub-lethal consequences on the biochemical profiles (i.e., the metabolome) of aquatic organisms and may be a concern for frog species that breed and develop in small, often ephemeral, waterbodies. Our study highlights the benefits of integrating untargeted metabolomics with other ecological and toxicological endpoints to provide a more holistic characterisation of the sub-lethal impacts associated with bushfire-fighting chemicals and with environmental contaminants more broadly.