Thio-olivines such as (Fe,Mn)₂(Si,Ge)S₄ have been proposed as candidate earth-abundant materials for single and multi-junction solar cells. In this work we present the first investigation of Mn₂SiS₄thin films prepared by reactive magnetron sputtering deposition, using a composition grading approach. Precursor instability in ambient conditions is observed, revealing the oxidation/hydrolysis of Sisingle bondS bonds from the as-deposited film as a blocking mechanism for the ternary compound formation. Structural, morphological and optical properties of the annealed Mn₂SiS₄ films are reported for the first time. Resulting Mn₂SiS₄ films have orthorhombic Pnma structure and are polycrystalline. Raman active modes at 325 nm excitation are observed at 262, 320, 400 and 464 cm⁻¹. From room temperature photoluminescence at 532 nm excitation the band gap is estimated to be about 1.9 eV, but a high optical absorption coefficient of >10⁴ cm⁻¹ was only obtained at E > 2.8 eV. First principles calculations are used for better understanding of opto-electronic properties. From the calculations, Mn₂SiS₄ is suggested to have a band gap of about 1.73–1.86 eV depending on the magnetic configuration of Mn and slight indirect nature. The slow absorption onset is interpreted by strong anisotropy due to one of the components of the dielectric function.