Graphene nanoplatelets (GNPs) are recently developed nanoparticles that are formed by stacks of short disk-like layers of graphite. They cost considerably less than their carbon nanotubes (CNTs) counterparts, and can be potentially used to generate multi-functional material systems. However, there are significant number of structural differences between GNPs and CNTs. It is therefore timely to review and optimize the current processing techniques used for generating GNP-nanocomposites. In this research, a scalable shear mixing approach (i.e., a three-roll mill) is utilized for achieving uniform dispersion of different fractions of GNPs in an epoxy resin. Then, the stiffness, electrical and thermal conductivity, and linear coefficient of thermal expansion of the resulting nanocomposites were evaluated. The as-processed nanocomposites exhibited significant improvement in their thermal properties, but a moderate increase in stiffness. The electrical percolation threshold of the nanocomposite occurred at higher concentration of GNP than that predicted by the available micromechanical models. This is attributed to the change in size of GNPs, which occurs as a result of manufacturing process, as observed by scanning electron microscopy.