Research and development of graphene and graphene-based materials have been attracting significant interest since they were invented. This dissertation mainly focused on the graphene-based materials: (a) a fundamental understanding of nanosize functionalized graphene inclusions in resin and fiber systems, (b) the development of graphene based hierarchical nanocomposites incorporated with thin layers of graphene papers, and carbon and glass fibers, and (c) the mathematical modeling of a process that can be useful for aircraft and wind turbine applications. Dispersion, wet layup, and vacuum-assisted resin transfer molding (VARTM) processes were used in the fabrication process, and then mechanical, thermal, electrical, and electromagnetic interference (EMI) properties of the materials were characterized using various techniques. Results of experiments conducted at different concentrations, thicknesses, pressures, and types of reinforcement materials show that the graphene-based fiber composites provided substantially better physical properties than other conventional carbon and glass-fiber-reinforced composites because of the extraordinary physical properties of graphene nanoflakes, rate of dispersion, and stronger covalent bonding between the resin and the reinforcement systems. MESOTEX (MEchanical Simulation of TEXtile) was utilized to predict the bulk-scale elastic modulus of the graphene-based fiber-reinforced composites. Graphene nanoflakes are assumed to be randomly and homogenously distributed in Epon 862 epoxy resin. Halpin-Tsai theories/equations were first used to simulate the tensile modulus of two phase graphene-based polymeric nanocomposites; however, today’s nanocomposite materials have three-phase structures. MESOTEX modeling results on variable laminate composite geometries confirmed that this modeling had a good prediction on a three-phase nanocomposite system and the test results indicated the existence of agglomeration effects on the properties of nanocomposites.