α-MgAgSb shows promise as a potential new low-temperature thermoelectric (TE) material and has been widely researched recently. We explored the effects of sintering conditions on the properties of MgAgSb-based thermoelectric materials through manipulating a spark plasma sintering system (SPS), where Ag vacancies and Mg point defects play a dominant role. The transport properties of MgAgSb were optimized effectively and efficiently, especially for electrical transport. As a result, we obtained a steady power factor (PF) of ∼17 μW cm-1K-2, owing to the optimal carrier concentration of 9.8 × 1019cm-3. Additionally, α-MgAgSb exhibits an ultralow lattice thermal conductivity of around 0.45 Wm-1K-1at 375 K. More importantly, a high ZT value of 0.85 was achieved below 375 K, approaching room temperature.