Herein, garlic oil-functionalized onion-like carbon (OLC) nanoparticles were successfully prepared through a multistep process involving the carbonization of candle ash followed by surface modification. Initially, the OLC was prepared by heat-treating candle ash under 450 °C and then grafting polyethylenimine (PEI) using epigallocatechin gallate (EGCG) as a cross-linking agent. Subsequently, garlic oil was grafted onto PEI@OLC via the aza-Michael reaction with PEI, thereby obtaining garlic oil-functionalized OLC nanoparticles (GO@OLC). The GO@OLC exhibited enhanced lubrication properties as a lube additive, with a low coefficient of friction (COF) of 0.11 and a significant reduction of 76.57% in wear volume. The enhanced lubrication performance is credited to the rolling effect and surface repairing effect of the OLC nanoparticles as well as the formation of a complex protective layer by GO@OLC-induced tribochemical reactions.