The pyrolysis behaviors, the kinetics of the synergistic effects, the functional groups during the co-pyrolysis of torrefied-biomass (TBG) with a tire, and different plastics such as high-density polyethylene (HDPE), ethyl vinyl acetate (EVA), polystyrene (PS), polypropylene (PP) were analyzed by TG-FTIR. The TG-DTG curves revealed thermal stability due to torrefaction treatment and blending. The most potential reaction mechanisms associated with the first stage for both pure and blend samples were first-order reaction and one-dimensional diffusion mechanisms, while the second stage was mostly governed by second and third-order reaction mechanisms. The interactions between TBG-plastics/tire were obvious at temperatures of 290–540 °C, according to the variation of weight loss (ΔW) values. The highest degree of synergy was observed with the TBG/PS blend, while the TBG/tire mixture being the least synergistic. The FTIR spectra indicated that hydrocarbons compounds, CO2, CO, H2O, CH4, NH3, acid, aldehydes and C=O, C-O, O-H, C-H, C-C, N-H, HCN were the main gaseous products and functional groups detected by the FTIR. The HDPE, EVA, and PP generated mainly alkanes and alkenes. While the PS depolymerized into styrene monomers. The tire mainly disintegrated into olefins and alkanes. The effect of co-pyrolysis of TBG, tire, and different plastics on species produced is noticeable on pyrolysis characteristics, kinetics, gaseous products, and functional groups. Thus, H2O, acid, ketone, and aldehydes were suppressed. Generally, the co-pyrolysis of plastic/tire with TBG can reduce the oxygen-containing compounds in the gaseous species and can improve the release of hydrocarbons.