Porphyrin derivatives are popular photodynamic therapy (PDT) agents; however, their typical insolubility in water has made it challenging to separate cells of organisms in a liquid water environment. Herein, a novel water-soluble 5,10,15,20-tetrakis(4-methoxyphenyl-3-sulfonatophenyl) porphyrin (TMPPS) was synthesized with 95% yield by modifying the traditional sulfonation route. The reaction of TMPPS with AgNO₃ afforded AgTMPPS an unusual Ag(II) oxidation state (97% yield). The free base and Ag(II) complex were characterized by matrix-assisted laser desorption ionization-mass spectroscopy, and ¹H nuclear magnetic resonance, Fourier-transform infrared, UV-vis, fluorescence, and X-ray photolectron spectroscopies. Upon 460 nm laser irradiation, AgTMPPS generated a large amount of ¹O₂, whereas no ⦁OH was detected. Antibacterial experiments on methicillin-resistant Staphylococcus aureus (MRSA) revealed that the combined action of Ag^Ⅱ ions and PDT could endow AgTMPPS with a 100% bactericidal ratio for highly concentrated MRSA (10⁸ CFU/mL) at a very low dosage (4 μM) under laser irradiation at 360 J/cm². Another PDT response was demonstrated by photocatalytically oxidizing 1,4-dihydronicotinamide adenine dinucleotide to NAD⁺ with AgTMPPS. The structural features of the TMPPS and AgTMPPS molecules were investigated by density functional theory quantum chemical calculations to demonstrate the efficient chemical and photodynamical effects of AgTMPPS for non-invasive antibacterial therapy.