This study addresses the limited understanding of the structural performance of composite sandwich façade panels made with glass and pultruded glass fiber-reinforced polymer (GFRP), which represent a promising alternative to conventional aluminum glazed systems. These panels, measuring 1300 × 600 mm, were experimentally tested under monotonic flexural loading to explore the influence of adhesive type on structural performance, comparing assemblies bonded with silicone-based adhesives to those bonded with epoxy-based adhesives. An initial-stage ANSYS FE model was developed and validated against the experimental results, providing further confidence in the findings and enabling predictive analysis. Key focus areas include analyzing the flexural response and investigating shear lag effects, which are critical to understanding the effective widths and mechanical behavior of glazed composite sandwich panels. The findings highlight that epoxy-bonded panels demonstrate significantly greater stiffness and load-bearing capacity compared to silicone-bonded panels, underscoring the importance of adhesive properties in achieving optimal performance. This research contributes to the development of analytical models that can accurately predict the behavior of glass-GFRP composite panels, providing engineers and designers with essential insights into the mechanical performance of such systems. By demonstrating the feasibility of replacing traditional aluminum unitized curtain walls with glass-GFRP sandwich panels, this study illustrates the potential to create slimmer, stronger, and more durable façade systems with enhanced corrosion resistance. These findings support the transformative role of composite materials in advancing façade panel design for minimalist, sustainable, and architecturally innovative building exteriors.