Bilayer and multiple layers of two-dimensional materials exhibit sliding ferroelectricity due to the asymmetric interlayer orbital hybridization. The spin degree of freedom can be used to tune the interlayer orbital hybridization and hence the interlayer charge transfer. In this work, we utilize the bilayer of magnetic two-dimensional MnNiP2 S6 to demonstrate the idea. First-principles calculations confirm that the out-of-plane polarization depends on the magnetic configuration. A supersuperexchange path across the van der Waals gap with all the bond angles close to 180° is responsible for the interlayer exchange interaction and the spin-dependent interlayer charge transfer. This work provides a promising route for constructing a multiferroic two-dimensional system by stacking nonpolar magnetic monolayers.