The accuracy of existing compressive strength models for fiber–reinforced polymer (FRP)-confined concrete might vary significantly since most of them were established empirically, without a clear understanding of the confinement mechanisms. Previous studies have suggested that the compressive behavior of confined concrete depends on its confining stress path. However, the confining stress path of FRP-confined concrete and its corresponding effect on the behavior of FRP-confined concrete has not been investigated, to the best of the authors’ knowledge. In this paper, the confinement mechanism of FRP-confined concrete will be investigated for the first time by investigating the confining stress path and the relationship between the confining stress path and the compressive strength of FRP-confined concrete. The results indicate that the FRP-confined concrete that has different column parameters generally yields different confining stress paths, which leads to different compressive strengths. The influence of the confining stress paths on the compressive strength was observed to be less significant for the specimen that was confined by a stress path with a larger lateral stress dominant index. Based on the theoretical and experimental results of this paper, a confining stress path-based compressive strength model will be developed for FRP-confined concrete. The developed model yielded more accurate predictions than existing models based on the results of this paper and previous tests.