A promising area in nanomedicine is the investigation of underused plants as sustainable resources for ecologically approachable synthesis of metallic and bimetallic nanoparticles. These plants have distinct phytochemical profiles full of alkaloids, flavonoids, terpenoids, and phenolic chemicals that act as organic reducing and stabilizing agents during manufacture. Because of their improved physicochemical characteristics, such as high surface area, catalytic efficiency, and stability, the resultant nanoparticles, especially metallic and bimetallic structures, have shown important biomedical applications. Compared to their monometallic counterparts, bimetallic nanoparticles exhibit higher efficacy in targeting human pathogens and cancer cells due to their synergistic effect, which combines the capabilities of two metals. This chapter examines developments in the environmentally friendly synthesis of metallic and bimetallic nanoparticles from underutilized species and assesses potential uses in biomedicine, modes of action, and human health in the future. The difficulties associated with clinical translation, biological activities, and characterization methods are given attention. Utilizing the underutilized plant-derived nanoparticles provides a novel and sustainable approach to treating a wide range of human illnesses.