A robust multiferroic material has been synthesized through an interface-modulated chemical vapor deposition (CVD) method, producing a 1-inch one-unit-cell of non-layered chromium sulfide (Cr₂S₃) with unidirectional orientation on c-plane sapphire. The interfacial interaction between Cr₂S₃ and the sapphire substrate induces intralayer sliding of self-intercalated Cr atoms, breaking the space reversal symmetry and enabling robust room-temperature ferroelectricity with a remanent polarization that persists for over a month. Additionally, long-range ferromagnetic order is observed with a Curie temperature approaching 200 K, nearly double that of the bulk counterpart. The material also exhibits strong magnetoelectric coupling, making it the largest and thinnest multiferroic material to date. The synthesis method enables the growth of wafer-scale single crystals, providing a platform for high-performance spintronic and magnetoelectric devices. The study demonstrates the potential of Cr₂S₃ as a promising candidate for next-generation information storage technologies. The results highlight the importance of interfacial engineering in achieving stable and scalable multiferroic materials.A robust multiferroic material has been synthesized through an interface-modulated chemical vapor deposition (CVD) method, producing a 1-inch one-unit-cell of non-layered chromium sulfide (Cr₂S₃) with unidirectional orientation on c-plane sapphire. The interfacial interaction between Cr₂S₃ and the sapphire substrate induces intralayer sliding of self-intercalated Cr atoms, breaking the space reversal symmetry and enabling robust room-temperature ferroelectricity with a remanent polarization that persists for over a month. Additionally, long-range ferromagnetic order is observed with a Curie temperature approaching 200 K, nearly double that of the bulk counterpart. The material also exhibits strong magnetoelectric coupling, making it the largest and thinnest multiferroic material to date. The synthesis method enables the growth of wafer-scale single crystals, providing a platform for high-performance spintronic and magnetoelectric devices. The study demonstrates the potential of Cr₂S₃ as a promising candidate for next-generation information storage technologies. The results highlight the importance of interfacial engineering in achieving stable and scalable multiferroic materials.