This article presents the application of agro-waste materials (i.e., bagasse and corn stalk fibers) along with E-glass fiber in order to evaluate and compare their suitability as reinforcement for thermoplastic composites. The hybrid effect of glass and cellulosic fibers on the tensile, flexural, and impact properties of the composites were investigated. Water absorption and thickness swelling were also studied. In general, the hybrid composites presented superior properties compared to the control (without glass fiber) samples. Additionally, synergistic improvements in the physico-mechanical properties of composites were obtained with the addition of glass fiber. Overall trend shows that with the addition of agro-waste materials, tensile and flexural properties of the composites were moderately enhanced. However, corn stalk fibers showed superior mechanical properties due to their high aspect ratio and chemical characteristics. Addition of glass fibers into the composites considerably enhanced tensile, flexural, and impact properties without having significant effect on the elongation at break. Morphological study also confirmed the impact behavior of composites. Moreover, incorporation of glass fiber with agro-waste fibers in PP matrix considerably decreased the water uptake and thickness swelling of the hybrid composites.