Fiber-reinforced composites have many advantages over conventional engineering materials. However. the intrinsic inhomogeneities of fiber-reinforced composites have made the prediction of the mechanical behavior of such a material a great challenge over the past three decades. In this dissertation, a micromechanical-based computational model within the context of finite element method is developed so as to predict. the overall elastoplastic behavior of n-phase fiber-reinforced composite with degrading matrix phase due to void growth. The computational micromechanics framework is based on the Transformation Field Analysis which takes into account the microstructure of the individual phases. The evolution of porosity is governed by the rate of void growth and the yield criterion is based on the model proposed by Gurson-Tvergaard. To integrate the overall governing equations, an implicit. stress integration scheme based on a modified Governing Parameter Method is employed to replace the explicit integration scheme commonly used and documented in the literature. The evaluation and verification of the proposed computational framework is carried out by comparing the results with numerical and experimental case studies published in the literature. In addition, an extensive parametric study has been completed to study the influence of the governing parameters on the overall mechanical behavior of fiber-reinforced composites. Finally, to demonstrate the application of the proposed methodology, the proposed constitutive model has been implemented in a finite element commercial software to study the effect of impact loading on particle-reinforced composite structures.