Antibacterial wound dressing is essential for inflammation control and accelerated wound healing. This study investigates polyzwitterion-functionalized silver nanoparticles (AgNPs) with enhanced antibacterial performance in an injectable wound dressing hydrogel. A mussel-inspired poly(sulfobetaine methacrylate-co-dopamine methacrylamide) (PSBDA) copolymer consisting of sulfobetaine and catechol moieties is developed and used in the stabilizing strategy for a facile one-step synthesis of AgNPs. The catechol moieties in PSBDA reduce AgNO3 in an alkaline solution and anchor PSBDA onto the surface of AgNPs. The zwitterionic AgNPs exhibit a uniform size profile and significantly improved stability, which are critical for maintaining antibacterial efficiency in a physiological environment. An injectable wound dressing hydrogel is developed by incorporating zwitterionic AgNPs into the mixed precursors of gelatin methacryloyl (GelMA) and poly(vinyl alcohol) (PVA). The hydrogel precursors exhibit good injectability and rapidly respond to UV-induced in situ gelation. The zwitterionic AgNP-incorporating hydrogel demonstrates significantly improved antibacterial efficiency compared to the non-zwitterionic counterpart both in vitro and in vivo. The zwitterionic modification also provides enhanced hemocompatibility and biocompatibility. The as-developed hydrogel dressing facilitates the resolution of inflammation and results in a rapid re-epithelization for the accelerated wound healing process in a rat full-thickness wound model.