Globally, there is a move towards using local, native species for ecotoxicological risk assessments. Anthropogenic stressors from urban, agricultural, and industrial activities can impact the health of receiving ecosystems. Biomarkers can provide valuable insights as early warning signals of the potential environmental impacts of stressors. The aim of this study was to develop biomarkers in the green-lipped mussel (Perna canaliculus), a potential bioindicator of environmental health for coastal marine ecosystems in New Zealand. Reverse transcription quantitative polymerase chain reaction (RT-qPCR) assays targeting the expression of genes involved in oxidative stress, xenobiotic transfer, membrane transportation, cellular and DNA response/repair, and endocrine disruption were developed and validated for P. canaliculus. We found significant modulation of genes associated with oxidative stress, xenobiotic transfer, membrane transport, endocrine disruption, and genotoxicity in P. canaliculus following 48-hour exposures to copper and benzoαpyrene. These results demonstrate the potential of P. canaliculus as a bioindicator species for environmental risk assessment. The gene expression assays showed potential as early indicators of exposure to the chemicals tested but require additional validation to assess their ability to predict effects at higher levels of biological organisation.