This study investigates the catalyzed and un-catalyzed pyrolysis kinetics of waste samples composed of a commercial mixture of high-density polyethylene (HDPE) and polypropylene (75:25 wt%). The reaction mechanism and kinetic compensation effects were examined. Thermal analysis was conducted at various heating rates (β = 2–20°C/min) in an inert atmosphere using thermogravimetric analysis (TGA). Four methods—Friedman (FR), Ozawa-Flynn-Wall (OFW), Kissinger-Akahira-Sunose (KAS), and Starink (ST)—were employed to evaluate the kinetic parameters, including the pre-exponential factor and activation energy. Additionally, five model-fitting methods (Coats-Redfern, master plots, and iteration methods) were used to establish the kinetic model. The conversion function for random scission processes, f(R), is proposed to accommodate degradation mechanisms. The addition of a 10 wt% Zeolite A catalyst significantly reduced the activation energy required for the degradation of the waste mixture.