Significant strides have been made in enhancing the thermoelectric properties of p-type PbTe alloys, whereas the thermoelectric performance of n-type alloys lags behind that of p-type alloys, primarily owing to the difficulty of improving their Seebeck coefficient via band convergence. In this work, Mn was introduced into the n-type Pb_0.985Sb_0.015Te alloy, and Mn doping increases the absolute value of the Seebeck coefficient significantly by increasing the effective mass and reducing carrier concentration, resulting in a higher power factor of 20.8 μW/K²cm being achieved for 0.5% Mn-doped sample at 573 K. Additionally, the decrease in electronic thermal conductivity, combined with the reduction in lattice thermal conductivity caused by the strengthened point defect scattering, leads to a significant decrease in the total thermal conductivity of the sample. And the lowest total lattice thermal conductivity of 1.16 Wm⁻¹K⁻¹ for a 2.0% Mn-doped sample has been achieved at 773 K. In the end, a maximum zT of 1.0 (773 K) and zT_ave of 0.62 (323–773 K) are attained in 1.0% Mn-doped Pb_0.985Sb_0.015Te alloy.