In this work a RVE finite element (FE) model was built for UHMWPE composite laminates. These materials consist of UHMWPE filaments and an optimised polyurethane matrix. Experimental studies found in the literature indicate that UHMWPE fibres experience a transversely isotropic viscoelastic-plastic behaviour. A three-dimensional constitutive model was developed and implemented in the LS-DYNA explicit FE code, through a user-defined subroutine, in order to describe the response of the fibre. The viscoelastic behaviour was coupled with a continuum damage mechanics approach while energy dissipation associated with failure was controlled through an objectivity algorithm to provide mesh insensitive solutions. A generic thermoplastic polyurethane material was used in the material model, due to confidentiality constraints. A strain-rate dependent elastic-plastic material model was chosen to simulate the behaviour of the resin. Interactions between the fibres and the resin were simulated using penalty-based cohesive contact algorithms within the LS-DYNA code. UHMWPE laminates possess a high fibre volume fraction, typically exceeding 80%, and are manufactured in a [0/90]2 ply configuration. Images from dark field microscopy have revealed a random fibre packing sequence through the thickness of each ply, as well as a variation in the cross-sectional shape of the fibres. In order to understand the effects of the microstructure morphology on the macro-scale mechanical response of the composite, both observations have been taken into account within the FE based RVE model. Moreover, the effect of interface defects has been studied by randomly varying the strength of the cohesive contacts in the RVE model. The micromechanical behaviour of the laminate was investigated under low and high strain-rates with special consideration given to the non-linear in-plane shear response. The predicted numerical response was validated against experimental results found in the open literature.