Silver nanoparticles (Ag NPs) were reduced on the surface of magnetic sporopollenin (Fe3O4@SP) modified with poly-dopamine to enhance the degradation capability for Rhodamine B (RhB). The polydopamine-coated Fe3O4@SP (PDA@ Fe3O4@SP) acts as a self-reducing agent for Ag+ ions to Ag0. The structural properties of the synthesized nanocomposite were determined using Fourier transform infrared spectrometry (FTIR), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD), inductively coupled plasma mass spectrometry (ICP-MS), and vibrating sample magnetometer (VSM). The systematic study of the degradation process was performed using Response Surface Methodology (RSM) to determine the relationship between the four process variables, namely, initial RhB concentration, NaBH4 amount, catalyst amount, and time. Optimum points were determined for these four parameters using both matrix and numerical optimization methods. Under optimum conditions, RhB was decolorized with a yield of 98.11%. The apparent activation energy (Ea) and rate constant (k) for the degradation were 24.13 kJ/mol and 0.77 min−1, respectively. The reusability studies of the Ag@PDA@Fe3O4@SP exhibited more than 85% degradation ability of the dye even after five cycles. As a result, Ag@PDA@Fe3O4@SP possessed high catalytic activity, fast reduction rate, good reusability, easy separation, and simple preparation, endowing this catalyst to be used as a promising catalyst for the decolorization of dyes in aqueous solutions.