PbTe‐based alloys have been widely used as mid‐temperature thermoelectric (TE) materials since the 1960s. Years of endeavor spurred the tremendous advances in their TE performance. The breakthroughs for n‐type PbTe have been somewhat less impressive, which limits the overall conversion efficiency of a PbTe‐based TE device. In light of this obstacle, an n‐type Ga‐doped PbTe via an alternative thermodynamic route that relies on the equilibrium phase diagram and microstructural evolution is revisited. Herein, a plateau of zT = 1.2 is achieved in the best‐performing Ga0.02Pb0.98Te in the temperature range of 550–673 K. Notably, an extremely high average zTave = 1.01 is obtained within 300 − 673 K. The addition of gallium optimizes the carrier concentration and boosts the power factor PF  =  S2ρ−1. Meanwhile, the κL of Ga‐PbTe reveals a significantly decreasing tendency owing to the defect evolution that changes from dislocation loop to nano‐precipitation with increasing Ga content. The pathway for both the κL reduction and defect evolution can be probed by an equilibrium phase diagram, which opens up a new avenue for locating high zT TE materials. A synergic approach, including defect engineering and carrier concentration optimization, to the fabrication of Ga‐doped PbTe thermoelectrics elicits reduced thermal conductivity and an enhanced power factor. It results in an extraordinary n‐type Ga0.02Pb0.98Te alloy, whose peak zT achieves 1.3 at 673 K. A phase diagram probes the best compositional region for the n‐type Ga‐PbTe alloys, in which the dislocation loop or nano‐precipitate forms.