The comprehensive study of waste industrial and automotive plastics [polypropylene (PP), polyethylene (PE), polystyrene (PS), ethylene-propylene copolymer (E/P), thermoplastic elastomer based on the ethylenepropylenediene terpolymer and polypropylene (PP/EPDM)] thermolysis processes with 0%, 10%, and 25% of equilibrium fluid catalytic cracking (FCC) catalyst content was performed, and the catalyst suitability for the thermolysis process was evaluated. The experiments were carried out in the fixed-bed reactor. Reaction time and product yields depend on the ratio of a catalyst and a feedstock. The catalyst used leads to the formation of branched C7-C9 hydrocarbons as the main products as well as to the increased content of aromatic compounds. According to the liquid products composition, it was determined that catalyst acidity is excellent only for PE thermolysis and that the products obtained from this raw material are liquid only in case of catalytic thermolysis. Aromatization indexes, competitive parameter, the relative amounts of aromatization and isomerization reactions, and the ratio of unsaturated and saturated hydrocarbons were estimated for nonaromatic raw materials to evaluate mechanistic pathways of the processes. It was determined that catalytic reactions mainly occur at the lower temperature, and they run via a free-radical mechanism as the reaction temperature increases. The kinetic and thermodynamic parameters were also estimated for all raw materials using thermogravimetric data, which appeared dependent on the catalyst/polymer ratio and the plastic type used. The appropriate amount of catalyst for each raw material was determined for the production of diesel and gasoline cuts.