Peptide-based hydrogels have gained considerable attention as a compelling platform for various biomedical applications in recent years. Their attractiveness stems from their ability to seamlessly integrate diverse properties, such as biocompatibility, biodegradability, easily adjustable hydrophilicity/hydrophobicity, and other functionalities. However, a significant drawback is that most of the functional self-assembling peptides cannot form robust hydrogels suitable for biological applications. In this study, we present the synthesis of novel peptide-PEG conjugates and explore their comprehensive hydrogel properties. The hydrogel comprises double networks, with the first network formed through the self-assembly of peptides to create a β-sheet secondary structure. The second network is established through covalent bond formation via N-hydroxysuccinimide chemistry between peptides and a 4-arm PEG to form a covalently linked network. Importantly, our findings reveal that this hydrogel formation method can be applied to other peptides containing lysine-rich sequences. Upon encapsulation of the hydrogel with antimicrobial peptides, the hydrogel retained high bacterial killing efficiency while showing minimum cytotoxicity toward mammalian cells. We hope that this method opens new avenues for the development of a novel class of peptide-polymer hydrogel materials with enhanced performance in biomedical contexts, particularly in reducing the potential for infection in applications of tissue regeneration and drug delivery.