Preparation and application of ecofriendly materials is becoming an urgent topic. In this work, a green approach for producing silver nanoparticles (AgNPs) embedded on natural Populus fibers (PF) was developed based on hydrothermal synthesis using polyamidoxime (PAO)-functionalized fibers (PF–g–PAO). Throughout the production process, PAO acts as a trapping, stabilizing, and reducing agent for AgNPs formation without involvement of any additional reagents. The effects of the hydrothermal synthesis temperature and PF–g–PAO immersion duration in silver ion solution on AgNPs formation were studied based on the morphology of the PF–g–PAO/AgNPs composites, and their application in catalytic reduction of 4-nitrophenol (4-NP) was investigated using scanning electron microscopy (SEM) and ultraviolet–visible (UV–vis) spectrophotometry. Under the optimal reaction condition, AgNPs with average size of 36 nm were embedded on the PF surface with high silver content (15.6 wt%), exhibiting high catalytic activity (2.40 s−1 g−1) and reusability (>5 cycles) in reduction of 4-NP to 4-aminophenol (4-AP). More importantly, the use of the renewable resource cellulose in this work represents a sustainable feature to reduce manufacturing cost and environmental impact.