Fibre-reinforced cementitious composite materials have been widely employed in recent decades to address the problems associated with conventional cementitious materials. The fibre–matrix bond is significant in composite materials because improving fibre–matrix interactions can improve the overall behaviour of the material. The primary goal of this study is to analyse the microstructure of the cement pastes produced using ordinary Portland cement and Portland pozzolana cement partially replaced by polypropylene fibres (0.05%), nano-clay (2%), and nano-silica (1%). The fresh properties of produced pastes, such as consistency and setting time, and at hardened state after 28 days of curing, SEM analysis and EDS tests were conducted to study their microstructure. From the obtained results, a higher consistency was observed due to the water absorption by the nanomaterials due to their larger surface area. The polypropylene fibres showed poor bonding properties with the cement matrix. The study also revealed that a small quantity of nanoparticles in cement and concrete composites enhances the nanostructure of cementitious materials, resulting in a denser matrix. The SEM images proved that the microstructure of samples with nano-clay and nano-silica has lesser pores and denser C-S-H. Nano-silica improved cement hydration and reacted with calcium hydroxide to form additional C-S-H gel. The EDS results corroborate the results of SEM.