Walnut protein beverages frequently undergo phase separation and quality degradation owing to insufficient colloidal stability. This study employed walnut protein–procyanidin covalent complex-based Pickering emulsions (WP-PC-PE) as a natural stabilizer to enhance beverage quality. Formulation was optimized using response surface methodology, yielding optimal parameters: walnut-to-water ratio 1:5.376, sucrose 1.885%, and WP-PC-PE 0.103%, with a predicted sensory score of 90.963. WP-PC-PE-fortified beverages exhibited superior sensory acceptance, elevated absolute zeta potential, viscosity, brightness, and stability coefficient, alongside reduced centrifugal sedimentation. Antioxidant activity and volatile flavor profile were also improved. During 14-day storage at 4, 25, and 37 °C, WP-PC-PE effectively mitigated pH drop, color fading, viscosity loss, and phase separation. The final product complied with microbiological and physicochemical standards. These findings demonstrate that WP-PC-PE is a favorable natural stabilizer for enhancing the quality and short‑term storage stability of walnut protein beverages.