In this article, we report the elastic, electronic, optical and thermoelectric properties of recently synthesized K2Cu2GeS4 chalcogenide. The structural parameters are found to be in good agreement with experimental results. The calculated single crystal elastic constants (Cij) show that K2Cu2GeS4 is mechanically stable. The investigated electronic band structures reveal semiconducting characteristics and are consistent with experiment. Important optical constants such as dielectric constants, refractive index, absorption coefficient, photoconductivity, reflectivity and loss function are calculated and discussed in detail. Optical conductivity is found to be in good qualitative agreement with the results of band structure calculations. The Seebeck coefficients for TB-mBJ potential within the studied temperature range vary from ∼450 to ∼200 μV/K. The anisotropic electrical conductivity and electronic thermal conductivity are observed in the layered structured K2Cu2GeS4. The power factor and electronic thermal conductivity at 800 K along xx-axis using TB-mBJ potential are found to be ∼6 μWcm−1K−2 and 0.578 Wm−1K−1, respectively and the corresponding thermoelectric figure of merit is 0.81. The obtained results predict that K2Cu2GeS4 is a promising material in thermoelectric device applications.