Nanomaterials, owing to high surface area and nanoscale size, have unique physical and chemical properties that can be engineered with construction material to achieve novel properties. As such, the present study examines stand-alone and the synergetic effect of incorporating nanomaterials in cementitious mortars subjected to an aggressive environment. For stand-alone effect nano-silica was considered, and for synergetic effect nano-silica along with nano-alumina were considered. Specimens were cured in potable and sulphate water to examine their comparative strength and durability performance for various duration. Strength parameters, for example, compressive strength and flexural strength were examined. Experiments such as water absorption, sorptivity, and mortar bar expansion were conducted according to American Society of Testing Materials (ASTM) standards. For the hydrated cementitious mortar products, scanning electron microscopy (SEM) analysis was performed. Research examination revealed cementitious composites with enhanced strength and durability, especially specimens with nano-silica particles. These results were also evident from microstructural analysis for the hydrated composite cement mortar products. Therefore, it is possible to develop mortars as smart mortars by engineering nano-particles into the mix.