Metal oxide nanoparticles (MONPs) have attracted considerable attention in recent decades due to their unique structural, electronic and biological properties. Among them, nickel oxide (NiO) nanoparticles stand out as versatile materials with a broad range of applications including catalysis, energy storage, sensors, electrochromic devices, and increasingly, biomedicine. Antimicrobial resistance (AMR) poses a global health challenge, and NiO nanoparticles have emerged as promising candidates for antimicrobial applications owing to their low cost, ease of synthesis, and potent activity against a wide range of bacterial strains. This review provides a comprehensive overview of NiO nanoparticles with special focus on their synthesis methodologies, physicochemical characterization, antimicrobial mechanisms, comparative antibacterial activities, and biomedical applications. In addition, challenges related to toxicity, environmental safety, and clinical translation are critically discussed. Future prospects for the rational design of NiO nanostructures and their integration into advanced nanomedicine are also highlighted.