Studying biological invasions may further our understanding of how ecological and evolutionary processes shape patterns of diversity within species and communities. The ability of non-native species to persist and adapt to new environments is expected to rely on their genetic diversity. To understand what shapes their genetic structure we first need to have a detailed knowledge of their colonization history. In this study, we used Bayesian clustering, approximate Bayesian computation methods and network analyses to reconstruct the origin and colonization pathways of 23 populations of the wall lizard Podarcis muralis in England. We then inferred how genetic diversity is affected by the origin(s) and admixture of distinct genotypic lineages. Our analyses show that established populations in southern England originate from at least nine separate sources from native populations in France and Italy with substantial admixture of native lineages. Genetic diversity was significantly lower in the non-native populations and the loss of genetic diversity was also accompanied by increased hatching failure. However, populations introduced as recently as 25 years ago show evidence of having adapted to the cooler climatic conditions in the UK. This study thus demonstrates the importance of understanding colonization history for understanding the persistence and adaptation of non-native species.