Influence of tungsten disulfide particles (WS2) on the friction and wear behavior of Mg-AZ91 forms the objective of this work. Friction stir processing (FSP) has been used to fabricate FSP AZ91/WS2 composite with various FSP passes. The microstructures were studied using a optical microscope (OM), electron backscatter diffraction (EBSD), and scanning electron microscope (SEM). Hardness is measured using Vickers’s microhardness tester. The impact of WS2 on the friction and wear resistance of Mg-AZ91 were evaluated using a pin-on-disc apparatus under dry sliding conditions. The microstructure showed the grain refinement of FSP AZ91/WS2 composite, due to severe plastic deformation and dynamic recrystallization. An increase in the FSP passes has transformed the grain size from micron- to nano-level. The hardness of FSP AZ91/WS2 composite is increased to 122 HV, from 62.2 HV0.3 of Mg-AZ91. The improvement in the hardness is due to the reinforcement of WS2 and grain refinement. A significant improvement in the friction and wear resistance was achieved for Mg-AZ91 composites in contrast to FSP AZ91 and AZ91. SEM micro-images showed the transfer of wear mechanism from severe adhesive wear to mild adhesive wear.