Recycling wood/plastic composites in municipal and industrial wastes currently represents a challenge which needs to be overcome. In this work, we considered the concept of independent pyrolysis of wood and plastic in wood/plastic mixtures for enabling a versatile catalytic process design which is capable of producing recoverable final products from both components. In order to reveal the influence of plastic on wood pyrolysis, the pyrolysis of beech wood (BW, wood material) in a polyethylene (PE) melt (polyolefin material) was performed at 350 °C. The combined use of thermogravimetric analysis, product recovery studies, in situ radical characterisations, and microscopic analysis revealed the influence of the PE melt on the BW pyrolysis. More specifically, a physical prevention of the intermolecular condensation and hydrogen abstraction from PE pyrolysates in the liquid/solid phase was observed. These interactions enhanced the production of levoglucosan and methoxyphenols by factors of 1.7 and 1.4, respectively, during the BW pyrolysis in the PE melt. Based on these results, we concluded that the observed synergistic effects could potentially control the yield and quality of useful products, as well as the utilisation of mixed wood/plastic wastes, which cannot be effectively recycled otherwise.