Fiber reinforced polymer composites (FRPs) are widely utilized in various industrial fields due to their remarkable mechanical properties and low cost fabrication. However, typical FRPs cannot concurrently fulfill optical transparency and high mechanical strength, which are essential for transparent electronics and automotive applications. Here, we report a transparent FRP (GFRH) that exhibits high opto-mechanical properties by incorporating reinforced glass-fibers into refractive index-tunable epoxy-functionalized siloxane hybrid materials. To achieve transparent composites, we precisely control the refractive index of the siloxane matrix by adding an epoxy cross-linkable hardener. We compare the opto-mechanical properties of the GFRP according to various conditions in terms of curing method (thermaland UV-curing), fiber content (from 0 to 25 wt% of matrix), fiber length (from 0.08 to 3 mm), and fiber type (filament mat, glass-fabric, chopped strands glass-fibers, and milled glass). Finally, to obtain high-performance GFRP, we further optimize the composite structure with short fiber (5 wt% of chopped strands glass-fibers) and long fiber (10 layers of glass-fabric). The optimized composite exhibits high optical transparency (80% @ 550 nm) and mechanical properties (251 MPa flexural strength, 9 GPa flexural modulus and 3 H pencil hardness). Our transparent composite has significant potential for the application of FRPs to transparent electronics and automotive devices.