We report on the synthesis of the II‐IV‐N2 semiconductors ZnSiN2, MnSiN2, and the Zn1–xMnxSiN2 solid solutions by a one‐step solid‐state metathesis reaction. The successful syntheses were carried out by reacting the corresponding metal halides with stoichiometric amounts of silicon nitride and lithium azide in sealed tantalum ampoules. After washing out the reaction byproduct LiCl, powder X‐ray diffraction patterns were indexed with orthorhombic space group Pna21. Single phase products were obtained without applying external pressure and at a moderate reaction temperature of 700 °C. The resulting ZnSiN2 was found to consist of nano‐sized grains and needle‐shaped nano‐crystals. With increasing manganese content in the Zn1–xMnxSiN2 solid solution, we found the reaction product to be increasingly crystalline. Both the cell parameters and the bandgap values across the different compositions of the solid solutions change linearly. The sample Zn0.95Mn0.05SiN2 synthesized by means of solid‐state metathesis reaction is an intense red emitter with a broad emission maximum at λmax ≈ 619 nm when excited with ultraviolet light after annealing the sample at a pressure of 6 GPa and a temperature of 1200 °C.