Silver nanoparticle (AgNP)-based nanofluids have emerged as a transformative class of materials that leverage the unique antimicrobial, thermal, and catalytic properties of AgNPs for diverse biomedical and environmental applications. This chapter presents a novel, cost-effective methodology for synthesizing AgNP-infused nanofluids using cellulose fibers, achieving stable dispersions with NP sizes from 1.5 to 13 nm. The synthesized nanofluids exhibited exceptional antimicrobial efficacy against various bacteria, with minimum inhibitory concentrations (MICs) as low as 2–9 mg/L for Escherichia coli and Staphylococcus aureus. Beyond biomedical applications such as wound dressings, surgical implant coatings, and veterinary feed supplements, these nanofluids demonstrate significant potential in environmental remediation, including water purification and solar-driven desalination, achieving near-complete bacterial removal and enhanced photothermal efficiency. The incorporation of AgNPs into personal protective equipment and food packaging further extended their utility by enhancing antibacterial and filtration performance. Despite their promise, challenges related to viscosity, potential toxicity, and environmental impact necessitate optimized synthesis and green stabilization strategies. This study underscores the versatility of AgNP-based nanofluids and their scalability for industrial applications, paving the way for sustainable advancements in nanotechnology.