Predicting the shear resistance of reinforced concrete (RC) beams strengthened with externally bonded carbon fibre–reinforced polymer (CFRP) reinforcement presents a considerable challenge due to the complex nature of shear-resisting mechanisms, which is influenced by the brittle nature of these failures. As a result, developing a design model to predict shear resistance becomes essential. Building on the authors’ findings from a previous study, namely a multi-objective optimization of an unbiased model for externally bonded CFRP system contributions to shear resistance in RC beams, this paper further applies the predictive model by incorporating a reliability-based analysis. Although the proposed model has demonstrated superior performance compared to existing models, ignoring uncertainty factors can lead to unreliable predictions, which raises concerns regarding the potential failure of RC beams under anticipated loads. This study aims to calibrate a resistance reduction factor for the model, facilitating its integration into design practices that meet the reliability standards of design guidelines. By employing a probabilistic framework, the reliability of the model is assessed, accounting for variations in beam features, material properties, loading conditions, and model uncertainties. The calibrated resistance reduction factor offers engineers a reliable and cost-effective tool for designing shear-strengthened RC beams with externally bonded CFRP systems. Furthermore, the proposed design model, along with the calibrated factor, was validated using an available dataset and compared against existing models.