Predictions of future climate change include shifts in patterns of precipitation, evapotranspiration and water run-off, resulting in increased periods of drought as well as variability and intensity of rainfall events. In the United Kingdom, the non-native North American sunfish, pumpkinseed Lepomis gibbosus (L.), is expected to benefit from these changes. We examine how hydrological variability induced by predicted changes in climate will affect the dispersal and spread of pumpkinseed in England by: (i) determining the relationship between discharge regime and pumpkinseed propagule pressure; (ii) examining a newly-established pumpkinseed population following a flood event in 2007; and (iii) comparing the growth and life-history traits of this new population with fish collected from the source population to demonstrate how the pumpkinseed's life-history plasticity contributes to its success as a coloniser. Using Bayesian modelling, we determined that the number of pumpkinseed escapees is likely to increase with increasing discharge. The newly-established pumpkinseed population showed fast juvenile growth, early age at maturity and small size at maturity. These traits differed significantly from the source population, specifically total length (TL) means at ages 1 and 2 were significantly greater in the new population, whereas TL at age 4 was significantly greater in the source population, and a significantly higher proportion of mature females were found at smaller size classes in the newly established pumpkinseed population. This study demonstrates the potential link between hydrological variability (current and future) and the dispersal of non-native pumpkinseed, leading to the establishment of new populations.