The use of biosynthesized metallic and bimetallic nanoparticles (NPs) as biocides for plant protection has gained significant attention in recent years due to their potential for sustainable and ecofriendly crop protection. In this review article, we discussed the biosynthesis of metallic and bimetallic NPs using various biological sources such as plants, fungi, bacteria, and algae. We explore the plausible mechanisms behind the biocidal activity of these NPs, including their ability to disrupt cellular structures, inhibit enzyme activity, induce oxidative stress, and modulate plant defense responses. We also highlight the challenges and limitations associated with the use of biosynthesized NPs, including their potential toxicity to nontarget organisms, potential impact on soil health, and the need for standardized protocols for their synthesis and characterization. Additionally, we discuss the potential strategies for overcoming these challenges, including the use of biocompatible stabilizers, controlled release formulations, and targeted delivery systems. Overall, biosynthesized metallic and bimetallic NPs hold promise as effective biocides for plant protection, but further research is needed to fully understand their mechanisms of action, optimize their efficacy, and ensure their safe and sustainable use in agriculture. In addition to exploring the biocidal mechanisms and challenges of using biosynthesized metallic and bimetallic NPs for plant protection, this review also delves into the cost‐benefit analysis of their application in agriculture.