The objective of this research is to examine the micromachining responses of a hierarchical three-phase composite made up of microscale glass fibers that are held together by an epoxy matrix, laden with nanoscale graphene platelets (GPL). To this end, micromilling experiments are performed on both a hierarchical graphene composite as well as on a baseline two-phase glass fiber composite without the graphene additive. The composite microstructure is characterized using transmission electron microscopy (TEM) and scanning electron microscopy (SEM) methods. Tool wear, chip morphology, cutting force, surface roughness, and fiber–matrix debonding are employed as machinability measures. In general, the tool wear, cutting forces, surface roughness, and extent of debonding are all seen to be lower for the hierarchical graphene composite. These improvements are attributed to the fact that GPL improve the thermal conductivity of the matrix, provide lubrication at the tool–chip interface, and also improve the interface strength between the glass fibers and the matrix. Thus, the addition of graphene to a conventional two-phase glass fiber epoxy composite is seen to improve not only its mechanical properties but also its machinability.