Chronic venous insufficiency (CVI) is a highly prevalent vascular disorder characterized by impaired venous return in the superficial or deep veins. Although compression therapy remains the primary clinical intervention, the hemodynamic mechanisms through which it alleviates venous dysfunction and restores valve competence are still not fully elucidated. The aim of the study is to create a one-dimensional (1D) hemodynamic model of the lower-limb venous system in order to investigate the role of valves and external compression on flow and pressure distribution. The model was developed by extending the open-source numerical framework Nektar1D (King’s College of London), originally validated for arterial simulations, to include venous-specific features. We developed a detailed venous network encompassing the major deep and superficial veins of the leg, interconnected by perforators, and integrated collapsible vessel mechanics, dynamic valve behavior, gravitational effects, and the presence of muscle activity. Model validation was performed through comparison with in vivo measurements and previously published numerical and experimental data. Results showed that the inclusion of valves restored physiological pressure and velocity profiles and reduced reflux volume (0.668 mL in the femoral vein (FV)), while their absence led to abnormally high venous pressures, bidirectional flow in perforating veins and high reflux volumes (7.536 mL in FV). The model also demonstrated the role of perforators in promoting efficient deep venous return under healthy conditions. External compression was found to reduce reflux during muscle relaxation by increasing hydraulic resistance due to the cross-sectional area reduction in the superficial system, thereby indirectly enhancing return volume. The model reproduced in-vivo pressure measurements consistent with literature, where higher pressure peaks were observed in CVI patients compared to healthy subjects. The proposed framework provides a validated computational tool for studying venous hemodynamics and supports the optimization of compression-based therapeutic strategies in chronic venous insufficiency.