Metal-doped magnesium silicides are increasingly attractive for thermoelectric applications at high temperatures (500 - 800 K) due to their low density, large natural availability, non-toxicity, good thermal stability, and transport properties. Phase equilibria and thermodynamic properties of metal-doped magnesium silicides, Mg2Si: Xm (X = Ti, Cr, Mn, Fe, Nb, Co, and Sn; m = 0 - 0.04 moles), were investigated in this study. Stoichiometric amounts of Mg, Si, and metal-dopant Xm powders were mixed, and cold-pressed to form (2Mg + Si + mX) pellets. Sintering of the pellets was conducted at 700 to 900 K for 0 to 3 hours to obtain Mg2Si: Xm alloys. The surface morphology of the Mg2Si: Xm alloys were characterized using X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy methods. Heat capacity of Mg2Si:Xm alloys was measured using differential scanning calorimetry (DSC). Gibbs energy data of Mg2Si:Xm alloys as function of temperature are determined.