Understanding lineage- and sex-specific responses of invasive species, such as the European green crab (Carcinus maenas), is essential for accurately assessing invasion potential across variable environments. We investigated the thermal responses of the three genetic lineages currently present in Atlantic Canada: a cold-tolerant Northern lineage originating from northern Europe, a warm-tolerant Southern lineage from the Iberian Peninsula, and their Hybrid lineage. Adult crabs from each lineage were exposed to a gradient of nine temperatures (2 to 24 ºC), which includes conditions encountered across the Pacific and Atlantic Canadian coasts. We quantified multiple performance traits: activity and aggressiveness level, metabolic rate, feeding rate, and ammonium excretion. Thermal responses varied in a trait-specific and non-additive manner according to lineage and sex. The Hybrid lineage exhibited distinct, trait-specific responses compared to the Northern and Southern lineages, particularly at thermal extremes. Our results confirm that the southern lineage is warm-adapted and the northern lineage cold-adapted.Furthermore, females generally appeared more thermally sensitive, exhibiting reduced aggressiveness and a limited capacity to adjust metabolic rates at thermal extremes, despite relatively high feeding rates. In contrast, males displayed higher and less variable aggressiveness, with little change in this trait across the temperature range tested. Inter-individual variability exhibited sex-biased patterns that depended on lineage. Overall, our results highlight that thermal performance in C. maenas results from complex interactions among temperature, lineage, and sex. Accounting for these sources of intraspecific variation improves predictions of establishment success and persistence across heterogeneous environments, providing key insight into how invasive species expand.