This study investigated the effects of ultrasonic shot peening (USSP) treatment at various durations on the corrosion resistance and antibacterial properties of 304 Cu-bearing stainless steel (304-Cu SS). The results showed that USSP treatment refined the surface microstructure, enhancing hardness, wear resistance, and dislocation density. With longer treatment time, grain size decreased, and martensitic phase formation was promoted, improving mechanical properties. However, extended USSP treatment induced internal stresses, negatively affecting corrosion resistance. Cu addition to 304 stainless steel resulted in large Cu-rich phases, leading to uneven elemental distribution and reduced corrosion resistance. USSP effectively fragmented these phases, promoting a uniform distribution and enhancing the formation of a dense passive film, with the 304-Cu-5 min coupon showing the best corrosion performance. Cu also significantly improved antibacterial properties, demonstrating strong activity against Eescherichia coli and Staphylococcus aureus after 72 h. Overall, USSP treatment optimized both corrosion resistance and antibacterial performance, with the 5 min treatment providing the best balance.