To assess the colonization success of pumpkinseed Lepomis gibbosus on the Iberian Peninsula, life-history attributes of pumpkinseed populations from Spanish water bodies were compared to populations in the northern and southern parts of its native range, as well as to those of English water bodies where introduced populations have shown minimal natural range expansion. Discriminate function analysis using five population characteristics [mean age at maturity, mean total length (LT) at maturity, gonado-somatic index (IG), mean LT at age 2 years as an indication of juvenile growth rate and relative body condition] strongly differentiated populations from the four regional study areas. Spanish populations were early maturing, showed moderate juvenile growth rate and LT at maturity and high IG relative to the other population groups. Spanish populations matured significantly earlier than Canadian and English populations, but not southern U.S.A. populations. Spanish populations, however, had a significantly higher IG than southern U.S.A. populations, suggesting greater reproductive output. Considering these differences in the context of the Winemiller and Rose triangular life-history strategy model, the pumpkinseed exhibits ‘equilibrium’ life-history traits that have made other non-native fishes successful invaders in areas where habitat alteration has resulted in more predictable discharge regimes and water levels. Populations in Iberia, however, appear to have achieved their success by adopting a more ‘opportunistic’ life-history strategy than their native counterparts. High levels of life-history plasticity appear to contribute to the success of this species on the Iberian Peninsula.