Ternary nitride semiconductors with wurtzite-derived crystal structures are an emerging class of materials for optoelectronic applications compatible with GaN and related III-V compounds. In particular, II-IV-V2 materials such as ZnSnN2 and ZnGeN2 have been very actively studied for applications in photovoltaics and light emitting devices. However, many other possible wurtzite-derived ternary nitrides have not been reported, and hence their optical and electrical properties remain unknown. Here, we report on Zn2SbN3-the first Sb-based nitride and a photoactive semiconductor. Surprisingly, Zn2SbN3 contains Sb in the highest (5+) oxidation state, and in the unusual tetrahedral coordination. This new Zn2SbN3 material has a solar-matched 1.6-1.7 eV band gap and shows near-band-edge room-temperature photoluminescence, demonstrating its promise as an optoelectronic semiconductor. Finally, Zn2SbN3 can be synthesized at low temperature under a wide range of processing conditions, despite being metastable according to theoretical calculations. All these results, as well as the band position measurements, indicate that Zn2SbN3 is a promising emerging semiconductor for applications as an absorber in photovoltaic-and photoelectrochemical solar cells.