The development and advancement of cement-based composites has shown promise in recent years. It is important to examine new materials and technologies so that they can satisfy the ever-changing repair and strengthening application needs in the structural engineering field. This paper presents an experimental study on the behavior of reinforced concrete beams strengthened in shear using an externally applied fiber-reinforced cementitious matrix (FRCM). The first aim of this study is to investigate the effectiveness and the performance of the polyparaphenylene benzobisoxazole fiber-reinforced cementitious mortar (PBO-FRCM) system for shear strengthening. The second aim is to study the shear performance of the PBO-FRCM system in terms of the availability and absence of internal transverse shear reinforcements. A comparison study with previous experimental work and the relevant code is done to evaluate the shear performance of the PBO-FRCM system. The test results include the observed shear contribution of the PBO-FRCM system, the failure mode of the strengthened beams, and the influence of the internal transverse shear reinforcements on the shear performance of the PBO-FRCM system.