Understanding the role of the landscape matrix in species dispersal is important when targeting conservation and management strategies. This Research Note shows how least-cost modelling was used to assess invasive grey squirrel Sciurus carolinensis dispersal movements within the UK, with a focus on the county of Cumbria. Two major networks were identified separated by the Cumbrian Mountain range. This indicated that there may be multiple colonisation routes into the county. These findings were supported by evidence from DNA sequencing of seven grey squirrel populations. Least-cost model predictions were further validated through data from five Global Positioning System (GPS) collared grey squirrels. Buffered least-cost path analysis and the development of a least-cost corridor model enabled the most likely grey squirrel dispersal routes to be identified and validated using GPS data. To provide information on movements and land cover use, the individual movements of each squirrel were assessed. A case study was then used to highlight how the validated least-cost model can be applied to areas where red squirrels Sciurus vulgaris are still threatened by the invasive grey squirrel to provide information to target management and conservation actions. The findings should influence management strategies for grey squirrel control and conservation of the native red squirrels.