Pre-treated beef patties (BPs) face storage instability due to lipid/protein oxidation, microbial spoilage, and quality loss. Purple onion pulp (OP), a bioactive-rich product, offers potential as a natural preservative. This study evaluated the utilization of OP (2.5%, 5.0%, 10.0%) in BPs for refrigerated (4 °C) stability. The results showed that during storage, OP addition reduced the pH value, a* value, and b* value of beef, while cooking loss was not significantly affected. At the end of storage, the addition of 10.0% OP decreased the formation of metmyoglobin (MetMb), thiobarbituric acid reactive substances (TBARSs) (with a reduction rate of 15.96%), and carbonyl groups, and also inhibited spoilage bacteria. Sensory evaluation and texture analysis indicated that the addition of OP improved the hardness, juiciness, and odor of beef. Specifically, the incorporation of 10.0% OP extended the shelf life of BPs to 9 days, effectively improving their storage stability. Therefore, adding 10% purple onion pulp OP to BPs can improve the storage stability and sensory quality of refrigerated BPs.