Engineering materials from the nanoscale to the macroscopic scale in order to achieve strong optical activity is important for many scientific disciplines from chemistry to material science and physics. This thesis work aimed to develop by self-assembly optically active metamaterials composed of plasmonic nanoparticles embedded in a helicoidal architecture made of chitin nanocrystals, and to understand how the material interact with light to generate macroscopic circular dichroism. The material fabrication was based on a unique wet-chemistry synthetic pathway to incorporate achiral plasmonic nanoparticles, of silver and gold, into an optically inactive chitin-nanocrystal template. Spectroscopic characterisation of the composite materials, wherein plasmonic nanoparticles appear as a disordered ensemble, showed intense and well-distinguished bisignate circular dichroism spectroscopic line shapes in the vicinity of plasmonic resonance. Tuneable spectral features of such chiroptical properties were also realized, through the control of particle number density, size, and type. Possibilities of macroscopic optical activity arising from a seemingly completely disordered ensemble were assessed theoretically, with supportive evidence of numerical modelling and calculations based on plasmonic ensembles extracted from experimental chiral composites. These findings not only expanded the experimental accessibility of optically active plasmonic metamaterials, but also theoretically demonstrated that macroscopic optical activity could arise from apparently disordered systems, thereby promoting the understanding of chiral light-matter interactions.