Polypropylene (PP)/sisal fiber (SiF)/cellulose nanocrystals (CNC) hybrid composites were prepared at a variable weight percentage of SiF/CNC loading (29:1, 27:3, 25:5, and 23:7) using melt-blending technique followed by injection molding. The dispersion of the CNCs and SiFs within the nonpolar PP matrix was enhanced by using maleic anhydride grafted PP (MAPP) as a compatibilizer. Furthermore, the mechanical properties like tensile, flexural, and impact properties of the hybrid composites were evaluated. High tensile strength and modulus of 47.02 MPa and 2820.26 MPa, respectively, were observed for the hybrid composite with the incorporation of SiF/CNC (27:3 wt%) in the presence of 5 wt% MAPP. Additionally, an increment of 30.87% and 14.81% was observed for corresponding flexural strength and modulus as compared to their counterparts without MAPP. The elastic moduli obtained experimentally were compared with the theoretical elastic moduli using Cox-Krenchel and Ouali model in combination with the Halpin-Tsai model. Surface morphology by field emission scanning electron microscopy observed that the CNCs and SiFs were well dispersed within the PP matrix in the presence of MAPP. Differential scanning calorimetry thermograms showed no measurable changes in the melting temperature (T-m) of PP in PP hybrid composites; however, an increment in the crystallization temperature (T-c) was observed. The thermogravimetric analysis confirmed the enhancement in the thermal stability of PP hybrid composites due to the synergistic effect of hybridization within the PP matrix. Partial substitution of CNCs along with SiFs within the matrix polymer shows an increment in the stiffness of the hybrid composites as evident by dynamic mechanical analysis. Graphic abstract [GRAPHICS] .