A new polymer composite was produced by using biochar derived from the Palm Oil Mill Effluent (POME) filler and high-density polyethylene (HDPE). Biochar particles produced through carbonization of organic waste of POME was melt mixed with HDPE at different biochar loading in the internal mixer. 10 wt% addition of biochar showed comparable processing characteristics, flow-ability and chemical resistance, and an enhanced thermal stability, tensile strength and tensile modulus compared to the neat HDPE. The thermal stability was enhanced by 9.2% based on the remaining residue upon combustion, whereas the tensile strength and tensile modulus was improved by 12.1 and 27.5%, respectively. POME-based biochar showed good capability as reinforcing filler for HDPE due to its good dispersion and presence of interaction through HDPE chain penetration at surface porosity of biochar as observed under scanning electron microscope images. The utilization of POME-based biochar as filler in HDPE composite, has great potential to mitigate organic waste from palm oil industries into value-added product. Moreover, the usage of fillers from waste material such as POME reduces the reliance on mineral based fillers from non-renewable resources such as calcium carbonate and silica.