The co-pyrolysis of biomass and plastics presents a promising approach for generating hydrocarbon fuels and high-value chemicals while addressing environmental pollution concerns. This study investigates the pyrolysis process by examining mixtures of pine sawdust (PS) and high-density polyethylene (HDPE) with varying mass proportions and heating rates using analytical methods including thermogravimetric analysis and differential scanning calorimetry (TGA-DSC), thermogravimetry coupled with Fourier transform infrared spectroscopy (TG-FTIR) coupled analysis, pyrolysis gas chromatography-mass spectrometry (Py-GC-MS) and kinetic analysis. The study highlights the impact of heating rate on product distribution, with significant changes observed when the biomass ratio is at 30 %. Moreover, the addition of high-density polyethylene leads to an increase in polyol content in the liquid product. Analysis of product types reveals that plastics act as “hydrogen donors,” supplying hydrogen to biomass during co-pyrolysis, thus reducing oxygen chemicals. Results from the kinetic analysis show that the activation energy for co-pyrolysis is lower than individual pyrolysis, also indicating a synergistic effect. Overall, this research provides insights into the synergistic benefits of co-pyrolysis and establishes a theoretical foundation for advancing co-pyrolysis technology.