This study presents experimental results from four-point bending tests on eight RC beams, demonstrating that the use of ultra-high-performance fiber-reinforced cementitious composites (UHS-ECC) led to a modest increase in load capacity and reduced maximum deflection. Notably, when fiber-reinforced polymer (FRP)--reinforced UHS-ECC was bonded to the RC beam, the load capacity of formed composite beams was significantly improved. However, some debonding at the UHS-ECC/concrete interface compromised the effectiveness of the epoxy bonding. A three-dimensional finite element model was developed to analyze the strengthening system, accurately predicting load-deflection curves and revealing the cracking process. The model suggested that the FRP bar achieved 75% of its tensile strength, making it more effective than the FRP grid as reinforcement in the strengthening layer. Parametric studies demonstrated that the UHS-ECC/concrete bond property had a more significant influence on the composite beam behavior than the bond between the FRP bar and UHS-ECC. In conclusion, the proposed FRP-reinforced UHS-ECC system offers a promising solution for retrofitting deteriorating RC structures, significantly improving load capacity and structural performance. This research contributes to the ongoing efforts in structural engineering and construction to enhance the durability and longevity of RC structures in harsh environments.