Van der Waals (vdW) hetero-bilayers are emerging as unique structures to enhance the performance of two-dimensional (2D) layered nanomaterials for next-generation electronic and optoelectronic devices. In this work, we employ first-principles calculations to study the novel tetragonal ZnS/SnO hetero-bilayer (BL). The state-of-the-art computations based upon quasiparticle GW and Bethe-Salpeter equation (BSE) are utilized to study the electronic and optical properties of this novel vdW hetero-bilayer. We reveal that ZnS/SnO BL is a polarized semiconductor with a clear built-in electric field, and possesses a special band characteristic favorable for reducing the carrier recombination. It is also demonstrated that strain and external electric field are among the effective methods to modulate the electronic and optical properties of ZnS/SnO BL. Our work suggests that ZnS/SnO BL has an excellent optical absorption in the solar spectrum, rendering the material a viable candidate for optoelectronic applications, in particular for solar water splitting. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.