This study explores the enhancement of flexural performance in built-up steel sections retrofitted with Carbon Fiber Reinforced Polymer (CFRP). Built- up steel sections are widely used for their load-bearing efficiency, but aging infrastructure and the need for sustainable development call for effective retrofitting strategies to extend their service life and improve resilience. CFRP, known for increasing load-carrying capacity, flexural rigidity, and reducing deflection responses, presents a promising solution. The research involves a comprehensive experimental analysis following ASTM 370 standards to assess the impact of CFRP on load-carrying capacity, deflection response, and flexural rigidity of retrofitted beams compared to unreinforced ones. Findings indicate that CFRP retrofitting leads to significant performance improvements: load-carrying capacities increased to an average of 501.71 MPa, deflection responses decreased to 8.23 mm, and flexural rigidity enhanced to an average of 16,406.39 N/mm. The study highlights the correlation between CFRP thickness and performance metrics, emphasizing the need for precise application strategies. Recommendations include optimizing CFRP thickness, targeting critical areas, assessing welded joint capacities, and simulating damage scenarios to evaluate retrofitting effectiveness. This research advances the understanding of CFRP in retrofitting built-up steel beams, providing valuable insights for engineering practice, academic research, and potential impacts on industry standards and policies.