Cadmium sulfide nanoparticles (CdS NPs) have been employed in various fields of nanobiotechnology due to their proven biomedical properties. They are unique in their properties due to their size and shape, and they are popular in the area of biosensors, bioimaging, and antibacterial and anticancer applications. Most CdS NPs are generally synthesized through chemical, physical, or biological methods. Among these methods, biogenic synthesis has attracted more attention due to its high efficiency, environmental friendliness, and biocompatibility features. The green approach was found to be superior to other methods in terms of maintaining the structural characteristics needed for optimal biomedical applications. The size and coating components of CdS NPs play a crucial role in their biomedical activities, such as anticancer, antibacterial, bioimaging, and biosensing applications. CdS NPs have gained significant interest in bioimaging due to their desirable properties, including good dispersion, cell integrity preservation, and efficient light scattering. Despite these, further studies are necessary, particularly in vivo studies to reduce NPs’ toxicity. This review discusses the different methods of synthesis, how CdS NPs are characterized, and their applications in the biomedical field.