Freshened offshore aquifers (FOAs) have emerged as a potential unconventional freshwater resource that can supplement coastal water supply. FOAs consist of low-salinity pore water (<33 PSU) stored in unconsolidated sediments or sedimentary rocks beneath the seafloor, typically within ~50 km of the coastline. Their occurrence and extent are commonly investigated using the controlled-source electromagnetic (CSEM) method, which maps seafloor electrical resistivity, a physical material property influenced by porosity of the host rock, and temperature and salinity of the pore fluid. The CSEM method has proven particularly effective for identifying FOAs in a range of geological and hydrogeological settings. Here, we investigate whether FOAs are present beneath the formerly glaciated continental shelf offshore PEI. Two-dimensional electrical resistivity models were derived from a time-domain CSEM survey conducted in late 2021 in the Gulf of Saint Lawrence to image the subsurface to ~500 m below the seafloor. The models reveal laterally continuous resistive anomalies (30–60 Ωm) at depths of ~100–250 m below the seafloor, spatially coincident with redbed sandstones identified in offshore borehole data. These sandstones host PEI’s onshore aquifer system, and borehole-derived porosity values of 10–20%, combined with the observed electric resistivities and Archie’s law, imply pore fluid salinities of approximately 4–10 PSU. Independent three-dimensional numerical simulations of coupled variable-density groundwater flow and salt transport further support the interpretation that these resistive anomalies represent FOAs. Our results add to growing global evidence that FOAs are a widespread phenomenon and suggest that offshore groundwater resources may enhance regional water security.