Ferulic acid (FA) is a promising nutraceutical with well-documented antioxidant, anti-inflammatory, and antidiabetic properties; however, its therapeutic potential is limited by poor solubility, stability, and bioavailability. The present study aimed to enhance the biological efficacy of FA through the development of a novel ternary nanocomposite based on ferulic acid–grafted chitosan (F-g-Cs) reinforced with polyethylene glycol-coated nanoceria (PEG-nanoceria). The synthesized nanocomposites (nCFCs) were physicochemically characterized using UV–Vis spectroscopy, FTIR, XRD, SEM-EDX, TEM, and DLS. The nanoparticles exhibited nanoscale dimensions (hydrodynamic diameter: 77–92 nm; crystallite size: ∼15 nm) and positive zeta potential (+33.8 to +38.6 mV), indicating good colloidal stability. Incorporation of nanoceria significantly improved encapsulation efficiency (up to 90.3%), thermal stability, and in vitro gastrointestinal bioaccessibility of FA. Release kinetics followed the Higuchi model, indicating diffusion-controlled release. Biological evaluation demonstrated enhanced antioxidant activity (FRAP, DPPH, and ABTS assays), potent α-amylase and α-glucosidase inhibitory effects, increased glucose uptake in yeast cells (up to 63.2%), and significant suppression of LPS-induced nitric oxide production in RAW 264.7 macrophages without cytotoxicity. Notably, nanoceria-containing formulations exhibited superior performance compared to F-g-Cs alone, confirming a synergistic effect. Overall, the developed PEG-nanoceria/FA-chitosan ternary nanocomposite represents a promising multifunctional nanoplatform with improved stability and enhanced antioxidant, anti-inflammatory, and antidiabetic activities, offering potential for future pharmaceutical applications.