Glass fiber reinforced polymer (GFRP) composites are desirable material choices for ballistic armor applications as they absorb energy through laminate deformation, fiber/matrix interphase debonding, resin plasticity and fabric ply delamination. Thick section GFRP armor undergoes different phases of damage during a ballistic penetration event. The strike face primarily undergoes high strain rate crush and punch shear damage under hydrostatic compression, while the backside undergoes large deformation, delamination and in-plane tension. Traditional composite panels are comprised of a single fabric/sizing and resin through the entire thickness that are not optimized for energy absorption for each phase of damage. In this study, an 18 mm thick functionally graded (FGM) composite with an areal weight (AW) of 38 kg/m2 was designed by partitioning the armor into 2/3 strike face and 1/3 back face. This was compared to a Baseline VARTM panel made from 33 layers of 814 g/m2 plain weave (PW) S-2 glass fabric with a 463 sizing and SC-15 epoxy. The FGM panel graded the fabric architecture, AW and sizing into a 79 layer preform that is impregnated with a high toughness Drexel mPRS 20% epoxy capable of achieving fiber volume fraction of 65%. The strike face utilizes a 302 g/m2 8-harness satin S-2 glass fiber fabric with 933 sizing. The back face laminate was 11 layers of the PW. The strike face provided 25% reduction in penetration during Depth of Penetration tests at 1 km/s, while the back face thin laminate ballistic perforation tests increased V50 by 10% over the baseline composite. Ballistic testing of the functionally graded design showed a 34% increase in energy absorption at comparable AW or a 24% thickness and 14% AW reduction for equivalent levels of protection. These results show functionally grading the microstructure of the composite to optimize energy absorption based on damage modes is a promising material by design strategy to achieve significant weight savings.