This article investigates a permanent magnet vernier machine (PMVM) equipped with positive-mutual-coupling (PMC) winding. The conventional winding layout typically presents negative-mutual-coupling (NMC) among the three-phase windings due to the 120o spatial phase shift. It is illustrated that in the NMC winding, the q-axis self- and mutual phase flux linkages are superimposed on each other. In contrast, the proposed PMC winding exhibits counteracted q-axis self- and mutual phase flux linkages, which contributes to reducing the terminal voltage. The generic methodology to design PMC winding is presented and exemplified on a 24-slot, 5-armature pole pair, and 19- rotor pole pair PMVM. Finite element analysis shows that the proposed PMC PMVM could improve the rated power factor and widen the constant torque region. With reduced terminal voltage and more voltage margins, the PMC PMVM can employ a higher q-axis current to generate torque, thus significantly enhancing the output torque and power factor during field-weakening operations. As a result, the output power capability and constant power speed range (CPSR) are improved dramatically. Finally, a PMC PMVM prototype is manufactured to validate the efficacy of PMC winding in improving field-weakening and power factor.