An efficient nature inspired algorithm based on particle swarm optimization (PSO) is presented in this paper for the optimal design of planar multi-layered radomes for multiband applications. Material layer sequence and thickness profile are the two critical factors determining the position of passbands in the frequency range of operation as well as the transmission performance in those bands. These design aspects have to be appropriately optimized to achieve the desired performance, and it becomes a daunting task for radome designers when a comparatively large database of suitable materials is available in the solution space. Even though commercially available software packages provide options (like particle swarm optimization (PSO), genetic algorithm (GA), etc.) for the optimization of thickness profile, they do not have the functionality for optimizing the position of a specific material inside the multi-layered radome wall configuration. In this regard, the proposed PSObased algorithm automatically chooses suitable materials from the predefined database and optimizes the thickness for each layer, in order to achieve superior transmission in user defined passbands. Furthermore, the superiority of the indigenously developed algorithm over the optimization techniques available in full wave simulation software (FEKO) w.r.t. accuracy and computational efficiency is also established using suitable case studies and validations. Although PSO has been used in the context of radomes, its application for the simultaneous optimization of material layer sequence and thickness profile of multi-layered radomes is not reported in literature to the best of our knowledge.