Abstract Combined use of plastic and biomass wastes offers promising pathway for simultaneous energy production and waste disposal. In this article, the co-pyrolysis of pinewood and polycarbonate (PC) was performed in a fixed bed reactor to quantify their synergistic interaction on the product output and determine the effect of char intermediates on the synergistic effects. The extent of synergistic effects was obtained via a direct comparison of results from co-pyrolysis of pinewood–polycarbonate mixture with the weighted average values from pyrolysis of individual components. The observed synergistic effects were further examined from the influence of char intermediates using tailored feedstock configurations to gain more insights into the synergistic mechanism. The results showed co-pyrolysis resulted in enhancement by 33% in H2, 26% in CO, and 19% in total syngas yields compared to their weighted values from individual pyrolysis. Co-pyrolysis also exhibited superiority in energy recovery with the overall energy efficiency promoted from 42.9% to 48.6%. Deconvolution of synergistic effects revealed that pinewood char catalytically enhanced PC degradation, while the effect of PC char on pinewood pyrolysis was minimal. This article provides results on deconvolved understanding of synergistic effects in co-pyrolysis of lignocellulosic biomass and PC wastes, which is very helpful in designing clean and efficient energy recovery systems from these waste resources.