<p>Binary indium tellurides have garnered considerable interest as promising thermoelectric materials. Despite the favorable low thermal conductivity, the electrical transport of InTe is severely limited at low temperatures by strong ionized impurity scattering due to the intrinsic In¹⁺ vacancy defect. In this work, a series of La-doped InTe, i.e., InLa_<i>x</i>Te (<i>x</i> = 0, 0.02, 0.04, 0.06), are experimentally and theoretically studied. The defect formation energy calculation reveals that La serves as a donor defect with lower formation energy than the In¹⁺ vacancy. Experimentally, the carrier concentrations of the InLa_<i>x</i>Te decrease with increasing La content; the mobilities, however, are increased by La-doping due to the suppression of the ionized impurity scattering. For the thermal transport of pristine InTe, the machine learning interatomic potential is trained, and a very good theory-experiment agreement on the phonon and thermal transport-related properties is achieved. At higher La concentrations (<i>x</i> = 0.06), extensive in situ formation of an amorphous In₄Te₃ phase occurs, further reducing the lattice thermal conductivity from 0.75 to 0.57 W m⁻¹ K⁻¹ at 300 K. Through the synergistic optimizations of both electrical and thermal properties, a peak <i>zT</i> of ∼0.75 at 750 K is achieved in InLa_0.02Te, and an average <i>zT</i> of ∼0.3 over the 300–600 K temperature range is achieved in InLa_0.06Te. The presented methodology provides a viable path for enhancing the performance of InTe-based thermoelectrics.</p>