The opto-electronic and thermoelectric properties of the XIn2S4 (X = Zn, Cd) thiospinels are studied by employing the density functional theory (DFT) based methods. The stability of thiospinels has been confirmed by formation energy. Direct and indirect bandgap for ZnIn2S4 and CdIn2S4 respectively are observed. The values of band gaps that are determined with modified Becke and Johnson (mBJ) potential are good agreement with experimental values. The optical and thermoelectric properties are discussed in details. Our calculated values thermoelectric parameters such as ZT values equivalent to unity can be achieved for both thiospinel and make them promising candidate in energy harvesting devices.