A simple adduct from tin tetraiodide SnI4 and octasulfur S8, SnI4⋅(S8)2 (1), is obtained employing a facile reaction. The combination of Sn4+ ions with d10 electron configuration, acentric SnI4 tetrahedra, and lone‐pair effects of S8, makes 1 a phase‐matchable infrared NLO crystal with a moderate second‐harmonic generation (SHG) response and a very high laser‐induced damage threshold (LIDT), which is well confirmed by the DFT calculations. The adduct SnI4⋅(S8)2, obtained by a solid‐state reaction, shows a moderate nonlinear optical (NLO) intensity and a large laser induced damage threshold (LIDT). Its phase‐matchable character and wide IR transparency make it a very promising IR NLO crystal, comparable to the benchmark system AgGaS2 (AGS).