A reliability analysis was conducted based on the flexural strength recommendations provided by the ACI 440.1R-15 guide concerning the glass fiber-reinforced polymer-reinforced concrete (GFRP-RC) beams. A statistical investigation was carried out by compiling the dataset of 235 specimens from the technical literature on the model uncertainty of the beams to select the best probability distribution. As such, two failure modes of concrete crushing and GFRP rupture were examined. Reliability was analyzed using the first-order reliability method (FORM) via iHLRF algorithm. Importance sampling was also employed to determine the efficiency of the FORM. Findings reveal that the flexural requirements of ACI 440.1R-15 regarding the FRP-RC beams are conservative for both failure modes, particularly the GFRP rupture failure. Subsequently, importance vector α and sensitivity vectors δ and η were conducted to rank the effect of the most important random variables and their probability distribution parameters on the reliability index. Results from the importance vector α demonstrate that the random variable d is the most significant variable in both failure modes amongst the examined design variables. Thus, uncertainty contributed with d has the greatest effect on the reliability index. Moreover, based on the results from sensitivity vectors δ and η, varying the mean and standard deviation of the random variable ML leads to maximum change in total failure probability of the problem. Finally, strength reduction factors of 0.65 and 0.75 were respectively proposed through calibration so as to reach the target reliability index for GFRP rupture and concrete crushing.