In this study, an Fe3O4/Bi2MoO6/g-C3N4 magnetic composite photocatalyst was synthesized for the visible-light-driven photocatalytic degradation of sulfonamide antibiotics, specifically sulfamerazine (SM1). Characterization techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), photoluminescence spectroscopy (PL), UV-vis diffuse reflectance spectra (UV-vis), and the use of a vibrating sample magnetometer (VSM), were employed to analyze the fabricated samples. The composite exhibited efficient visible-light absorption and charge separation, with optimal photocatalytic performance achieved at a pH value of 9.0. The study reveals the importance of solution pH in the degradation process and the potential applicability of the composite for efficient magnetic separation and recycling in photocatalytic processes. The Fe3O4/Bi2MoO6/g-C3N4 magnetic composite photocatalyst demonstrated exceptional stability and recyclability, maintaining a high degradation efficiency of over 87% after five consecutive cycles. An XRD analysis conducted after the cycling tests confirmed that the composite’s composition and chemical structure remained unchanged, further supporting its chemical stability. This investigation offers valuable insights into the photocatalytic degradation of sulfonamide antibiotics using magnetic composite photocatalysts and highlights the potential of the Fe3O4/Bi2MoO6/g-C3N4 composite for practical applications in environmental remediation.