UHMWPE composites have been widely used in ballistic protection systems due to their exceptional properties, which combine low density and high strength. This work develops a RVE-based finite element (FE) model to understand how the microstructure of such composites affects the overall mechanical behaviour of the laminate. Special consideration is given to the strain-rate dependence of material properties, and the in-plane shear response. The RVE represents a [0/90] configuration with a random fibre packing sequence through the thickness of each ply, as well as variations in the cross-sectional shapes of the fibres. The uncertainty of interface properties and its effect on the overall mechanical response is also investigated. The response of the fibres is assumed to be viscoelastic-plastic and transversely isotropic, while the resin is modelled as a strain-rate dependent elastic-plastic material. Interfaces between the fibres and the resin as well as the interlaminar adhesion are assumed to behave cohesively. The fibre’s constitutive behaviour is implemented through a user-defined subroutine in the LS-DYNA explicit FE code, while the resin and the interface behaviour are simulated with already available models within LS-DYNA. The fibre model is calibrated using experimental results on single fibre relaxation, longitudinal tension and through-thickness compression. The resin’s numerical response is calibrated through tensile stress-strain results of a generic thermoplastic polyurethane material under different strain-rates. The numerical results generated by the RVE model are validated against experimental results found in the open literature. Our results can be used as inputs in a homogenised continuum level model, and can express the effects of uncertainties which propagate from the microstructure to the macro-scale response.