[en] This paper presents Density-Functional Perturbation Theory (DFPT) calculations on the electronic, vibrational, and electron–phonon (EP) coupling properties of the Mg2Si thermoelectric compound. The DFPT yields very satisfactory results for the electronic and vibrational properties when compared to experiment. Regarding the EP interactions, as far as we know, they have never been reported so far. We show that the EP interactions in Mg2Si mainly involve the silicon atom. This result explains the improvement of the thermoelectric properties of Mg2Si using a solid solution Mg2Si1−xAx, where A is a heavier atom than Si. By guiding the choice of the substitution site, the study of the EP coupling properties could be used in the search of new thermoelectric materials based on solid solutions.