The recently emerged ferromagnetic two-dimensional (2D) materials provide unique platforms for compact spintronic devices down to the atomic-thin regime; however, the prospect is hindered by the limited number  of ferromagnetic 2D materials discovered with limited choices of magnetic properties. If 2D antiferromagnetism could be converted to 2D ferromagnetism, the range of 2D magnets and their potential applications would be significantly broadened. Here, we discovered emergent ferromagnetism by interfacing non-magnetic WS2layers with the antiferromagnetic FePS3. The WS2exhibits an order of magnitude enhanced Zeeman effect with a saturated interfacial exchange field ~38 Tesla. Given the pristine FePS3is an intralayer antiferromagnet, the prominent interfacial exchange field suggests the formation of ferromagnetic FePS3at interface. Furthermore, the enhanced Zeeman effect in WS2is found to exhibit a strong WS2-thickness dependence, highlighting the layer-tailorable interfacial exchange coupling in WS2-FePS3heterostructures, which is potentially attributed to the thickness-dependent interfacial hybridization.