The percentage of bitumen in asphalt mixtures plays a crucial role in determining pavement performance throughout its service life. This study investigates the effect of varying bitumen contents on the mechanical behaviour and durability of asphalt mixtures. Three mixtures containing 4.7%, 5.1%, and 5.5% bitumen binder were evaluated through a comprehensive set of laboratory tests, including Marshall stability and flow, semi-circular bending, pressure aging vessel, wheel rutting, dynamic modulus, creep compliance, and fatigue performance tests, supported by finite element modeling. The nonlinear plastic behaviour and damage evolution were analyzed using the Perzyna-type viscoplastic model and Lemaitre’s isotropic damage model. Results indicate that mixtures with lower bitumen content (4.7%) exhibit earlier fatigue damage, while higher bitumen content (5.5%) leads to increased rutting and creep compliance. The 5.1% bitumen mixture demonstrated the most balanced performance, showing 40% less induced plastic strain damage than the 4.7% mixture and 27% less than the 5.5% mixture.