Yet little is known about the synergism of quaternary bio-based nanocomposite systems on cement mortar performance. For the first time, this research examines a quaternary nanocomposite comprising nano-chitosan, polyvinyl alcohol (PVA), polyacrylic acid (PAA), and silver nanoparticles (AgNPs) synthesized via ultrasonication and added to Ordinary Portland Cement mortar at 1.0 wt. % of cement. To study the effects of PVA and PAA on compressive strength, four systems (Za1–Za4) were fixed at nano-chitosan = 1.50 g and AgNO₃ = 10 mL while changing PVA content (0.25- 1.50 g) and PAA content (0.125-0.750 g) to a cement: sand ratio of 1:2.75 and w/c = 0.485. We compared these variables of compressive strength, water absorption, bulk density, and setting times. One-way ANOVA and Tukey's HSD confirmed that all the mixes were significantly different (p < 0.001). Results: The optimal mixture Za1 reported compressive strength 34.33 ± 0.058 MPa (4.7% increase), water absorption 2.77 ± 0.058% (31.7% reduction), bulk density of 2259 ± 1·0 kg/m³, and setting time prolonged by initial and final, respectively, with values of 12.9% and 7·7%. In situ formation of AgNPs was confirmed by X-ray Diffraction (XRD), and Za1 exhibited a dense and homogeneous microstructure as revealed by Scanning Electron Microscopy (SEM) micrographs. C-S-H nucleation, pore-filling, crack-bridging, and nano-crosslinking mechanisms serve the process of improvement.