In this paper, the synergic effects of carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs) on the mechanics, microstructure, and durability of cementitious composites were investigated. Furthermore, due to the high potential of CNTs and GNPs to agglomerate, a novel technique was proposed by utilizing the combined effect of Pluronic F-127 and Tributyl phosphate (TBP) while optimizing the effective factors such as surfactant concentration, sonication time, and temperature to achieve an affordable and compatible industrial scale-up method for a high-quality dispersion of CNT + GNP (50/50). The UV–Vis spectroscopy, optical microscopy image analysis, zeta potential, and bundle size measurements indicated that a high-quality CNT + GNP dispersion with a low agglomeration area and bundle size (<1.2% and 219 nm) was achieved with 10% Pluronic (wt% of nanoparticles) over 3 h of sonication at 40 °C with the presence of TBP (50 wt% of surfactant). Flexural and compressive tests of the reinforced cementitious composites using different CNT + GNP concentrations showed a significant improvement in mechanical behavior during different periods of hydration. The measured bulk density, none destructive ultrasonic, and capillarity tests also indicated a denser and improved composite microstructure for the CNT + GNP reinforced specimens. The formation of an adsorption layer due to the presence of phosphate and hydroxyl functional groups (proven by FTIR analysis) had positive effects on regulating the microstructures of the hydration crystals. The SEM, TGA, XRD, and EDX analysis results showed that CNTs + GNPs increased the hydration rate. Moreover, CNT + GNP reinforcement led to a significant reduction in carbonation depth. Ultimately, the results obtained demonstrate that an optimum concentration of CNT + GNP is around 0.5%.