Invasive alien species are a major threat to global biodiversity and result in adverse environmental and socioeconomic implications, such as reduced ecosystem services, landscape productivity, and costly eradication initiatives. The ability to monitor the extent and spread of alien species invasions provides valuable insight for the mitigation of these adverse implications. The generation of Earth Observation (EO) Sentinel sensor provides unprecedented freely available imagery, which is suitable for both local and regional invasive species monitoring. Specifically, its radar (S1) and optical (S2) sensors offer unique tandem datasets valuable for landscape analysis. Hence, we sought to determine the synergistic potential of fused S1 dual-polarized synthetic aperture radar (SAR) imagery with S2 optical imagery for invasive alien species detection and mapping. S1 and S2 imageries were fused at the feature level, and the support vector machine algorithm used for the multiclass image classification. Results indicated that the fusion of the S1 dual-polarized imagery with S2 optical imagery produced the highest classification accuracy (85%), whereas stand-alone S2 optical bands produced the lowest classification accuracy (79%). Findings from this study underline the significant synergistic potential and complementarity of new-age S2 optical imagery and dual-polarized S1 SAR imagery for invasive alien species detection and mapping. Due to large swath, higher pixel resolution, free availability, and possible tandem complementarity between optical and SAR sensors, we recommend Sentinel EO imagery as an economically viable option for the invasive alien species detection and mapping.