In the present study, highly efficient catalysts based on corncob were synthesized for the esterification process. The synthesized catalysts were characterized by BET, XRD, and FT-IR. The effect of catalyst impregnation, carbonation, and sulfonation was studied in detail. The highest conversion of oleic acid (similar to 94.4%) was observed using a catalyst synthesized at H3PO4 impregnation ratio = 1 and time = 5 h; carbonization temperature = 723 K and time = 8 h; sulfonation temperature = 393 K and time = 15 h. Further, the performance of the catalyst was studied for the esterification of fatty acids (FAs) and free fatty acids (FFAs) present in Karanja oil. The catalyst showed similar to 90% conversion of FAs/FFAs within 2 h at 338 K using a molar ratio of 1:10 (FA to methanol)/1:20 (Karanja oil to methanol) and a catalyst loading of 10 wt %. Furthermore, the reusability test of the catalyst revealed that it can be used for 20 times in a batch reactor to give similar to 90% conversion of the oleic acid.