The direct band gap semiconductors are exceptional for their use as solar cells and in most optoelectronic devices. Using the full-potential linearized augmented plane wave (FP-LAPW) technique, the structural, electronic, optical, and thermoelectric characteristics of novel La2CdX4 (X = S, Se, Te) semiconductors are studied. The electronic band profiles support the density of state calculations and demonstrate a direct band gap nature. These materials appear thermodynamically stable based on the calculated phonon dispersion plots and from their predicted negative formation energy values. Furthermore, the significant optical properties were computed and described extensively. The predicted energy loss function with a few prominent peaks corresponds well with the plasma resonance that occurs at plasma frequency. Based on the reflectivity spectrum, the materials under consideration could be used as UV shielding or anti-reflective coating materials. From the investigation of the calculated significant thermoelectric characteristics, the materials were proven to be appropriate for thermoelectric devices. The current research will support advancement of numerous promising semiconducting technologies and their applications in general.