Noncentrosymmetric (NCS) mixed-metal chalcogenides have attracted significant attention lately because of their structural multiplicities, strong second-harmonic-generation (SHG) efficiencies (d(ij)) and large laser-induced damage thresholds (LIDTs), which make them promising nonlinear-optical (NLO) materials in mid- and far-IR (MFIR) applications. In this work, a ternary mixed-metal material, Cd4GeS6, has been synthesized by reacting CdS with GeS2 via a solid-state method at 1273 K. It exhibits a unique tetrahedral-stacking NCS framework structure consisting of two types of [Cd2S7] asymmetric groups and dispersed GeS4 tetrahedra. Remarkably, Cd4GeS6 shows type-I phase-matching ability and achieves a desired balance between strong d(ij) (about 1.1AgGaS(2)) and large LIDT (about 3.6AgGaS(2)), demonstrating that this material satisfies the essential requirements as a promising MFIR NLO candidate. Moreover, theoretical calculations were performed for a better understanding of the structure-property relationships.