With cities growing at a rapid pace, animal species must either retreat to patches of intact natural habitat or adapt to novel conditions in urban areas. While this disturbance causes most species to be in local decline, some show specific behavioural plasticity, facilitating success in a new habitat. The Eurasian red squirrel (Sciurus vulgaris) is a common small mammal species which occurs in high numbers in urban environments. To determine which characteristics enable its success, we investigated space use and activity budgets of seven free-ranging individuals living in semi-natural and urban habitats within a large city. We did not find significant differences in animals’ space use between habitat types but tendencies towards smaller home ranges and increased home range overlap existed among individuals in the urban site. Squirrels differed between sites in both overall activity levels and temporal activity patterns: urban animals spent less time active and activity onset was later compared to semi-natural conspecifics. This is likely explained by a combination of dense and reliable supplementary food sources in the urban habitat, reducing foraging effort, and restrictions to movement imposed by higher fragmentation. Flexibility in space use and activity budgets, as well as the ability to exploit anthropogenic food sources and tolerate reduced habitat connectivity, are likely the most important factors contributing to the squirrels’ success in cities. Accordingly, these traits could be used as indicators of low sensitivity towards urbanisation when assessing other species’ potential resilience. However, they do not immunise squirrels against extirpation. Further research on individuals’ foraging ecology and population health may reveal possible threats to urban red squirrels and help predict their future persistence in this challenging habitat.