For the first time, quaternary chalcogenide CuNi2InS4 nanocrystals with a wurtzite structure have been designed and fabricated as a new magnetic semiconductor. The phase structure analysis suggests that the synthesized wurtzite CuNi2InS4 phase has a disordered structure in which Cu+, Ni2+, and In3+ ions share the same lattice site of the unit cell with a random cation distribution. The prepared CuNi2InS4 nanocrystals have uniform bullet-like morphology, small size distribution, good monodispersity, and high crystallinity. The magnetic properties investigation reveals that the wurtzite CuNi2InS4 nanocrystals can exhibit a weak ferromagnetic moment with the blocking temperature at around 13 K thanks to the disordered wurtzite structure and the high content of magnetic Ni2+ ions. As for the semiconducting properties, the as-obtained wurtzite CuNi2InS4 nanocrystals show a strong and broad visible light absorption and have a direct bandgap of 1.45 eV. Due to their favorable optical properties, the fabricated thin film of CuNi2InS4 nanocrystals exhibits a good photoelectric response to the solar spectrum, which makes the obtained new phase potential candidate for applications in the photovoltaics. This work demonstrates a new metastable I-II2-III-VI4 chalcogenide that can be used to render multiple functionalities and applications.