A micromechanics framework for modelling the longitudinal failure of unidirectional fibre composites, in both tension and compression, is presented. Appropriate constitutive models are used for the different constituents (i.e., fibre and matrix) and interfaces. An algorithm for the generation of the fibre misalignment is reported. It combines a stochastic process with an optimization procedure in order to match the numerical and experimental misalignment angle distributions. Two alternative strategies could be used for the optimization procedure, based on the minimization of the standard error of the likelihood or probability, respectively, whose pros and cons are discussed. Finally, micromechanical modelling in tension and compression are reported, and the influence of the fibre misalignment angle distribution is assessed.