Biological invasions are a key driver of global change, affecting biodiversity, community structure and ecosystem functioning in aquatic environments. Their dynamics and impacts may be further shaped by chemical contamination and other anthropogenic pressures, which can influence establishment, persistence, spread and the magnitude of ecological effects. In invaded ecosystems, non-native species often occur under multiple stressors, including habitat alteration, environmental variability, pollution and climate-related changes. Their success may therefore reflect not only biological traits and ecological opportunity, but also physiological plasticity and tolerance to disturbed conditions. This contribution explores aquatic non-native species as informative models for linking invasion ecology, contaminant exposure and ecosystem-health assessment. Selected case studies on invasive crustaceans and non-native bivalves are used to illustrate how biomarker-based responses can provide early-warning information on exposure, tolerance and sublethal biological effects under chemical and environmental stress. Oxidative stress biomarkers and detoxification-related responses are particularly useful for interpreting adaptive capacity, organism performance and ecological responses in impacted aquatic systems. Non-native species are not proposed as substitutes for native taxa, nor as conservation targets or indicators of pristine conditions. Rather, they can provide complementary information within integrated environmental monitoring approaches, especially where invasion success and contaminant pressure coexist. Integrating invasion ecology, biomarkers and environmental context can improve the assessment of invaded aquatic ecosystems and support more effective monitoring and management under global change.