The　development　of　Eu-based　chalcogenides　with　exceptional　nonlinear　optical　(NLO)　performance　in　the　infrared　(IR)　region　has　garnered　increasing　attention.　However,　the　design　and　synthesis　of　such　compounds　with　non-centrosymmetric　(NCS)　structures　remain　a　significant　challenge.　In　this　study,　we　report　the　successful　synthesis　of　a　novel　quaternary　Eu-based　chalcogenide,　β-EuZnGeS4,　achieved　through　an　isovalent　cation　substitution　strategy　starting　from　the　ternary　parent　compound　Eu2GeS4.　This　innovative　approach　induces　a　structural　transformation　from　centrosymmetric　to　non-centrosymmetric,　thereby　enhancing　the　NLO　properties.　β-EuZnGeS4　crystallizes　in　the　orthorhombic　Fdd2　space　group,　with　a　unique　two-dimensional　[ZnGeS4]2−　layer　structure　that　accommodates　Eu2+　cations.　Notably,　β-EuZnGeS4　exhibits　a　well-balanced　set　of　optical　properties,　including　a　remarkable　phase-matching　second-harmonic　generation　(SHG)　effect,　with　its　maximum　SHG　value　being　twice　that　of　AgGaS2　with　a　2050　nm　laser.　Additionally,　it　exhibits　a　high　laser-induced　damage　threshold,　surpassing　AgGaS2　by　a　factor　of　13.1,　along　with　a　broad　transparency　window　extending　from　0.39　to　23.7　μm.　Theoretical　calculations　further　reveal　that　these　outstanding　optical　properties　stem　from　the　synergistic　effects　of　the　highly　distorted　tetrahedral　[ZnS4]　and　[GeS4]　motifs　within　the　crystal　lattice.　This　work　not　only　expands　the　materials　database　for　rare-earth　metal　chalcogenides　but　also　provides　a　novel　strategy　for　designing　NCS　structures　with　tailored　optical　properties　for　a　wide　range　of　applications.　©　2025　The　Royal　Society　of　Chemistry.