The integration of biosensing platforms with drug delivery systems has led to effective treatment strategies for biomedical applications. With the emergency of nanotechnology, the manipulation of materials in the nanometer, these biosensing and drug delivery systems have been tremendously improved due to the exceptional properties exhibited by these materials. The conventional approaches used to synthesize the nanomaterials including physical and chemical methods involve the usage of harsh chemicals and hazardous reaction conditions and hence posing a threat to health and the environment. This problem is solved by the biological methods that involve green nanotechnology which integrates green chemistry and engineering principles to formulate harmless and eco-friendly nanomaterials to fight the complications affecting human health and the environment. These biological methods use phytochemicals found in plants and plants parts as well as microorganisms for the bioreduction of metal ions to their corresponding nanomaterials. The plants and the microorganisms are readily available, cost-efficient, and have biocompatibility hence offering sustainable synthetic methods for nanomaterials. This review will therefore focus on the plant-mediated and microbe-mediated green synthesis of different nanomaterials, the mechanisms of these synthetic methods, the application of the green synthesized nanomaterials in biosensing and drug delivery as well as the challenges of the synthetic methods.