The increasing generation of textile waste and the growing demand for sustainable materials have made the development of polymer composites reinforced with reused post-consumer textiles an important research area in recent years. In this study, sustainable thermoplastic textile composites reinforced with polylactic acid (PLA)/reused post-consumer denim fabric (RDF) and polypropylene (PP)/reused post-consumer denim fabric (RDF) were fabricated and characterized. Composite laminates were produced using the hot-pressing (compression molding) method, an industrially applicable and scalable manufacturing technique, without the use of chemical surface treatments or compatibilizer additives. The effects of matrix polymer selection and textile reinforcement architecture on the mechanical performance and environmental durability of the composites were systematically investigated through tensile, flexural, impact, and moisture absorption tests. The results revealed that PLA/RDF composites exhibited higher stiffness, with an elastic modulus of approximately 8.63 GPa, but displayed more brittle mechanical behavior. In contrast, PP/RDF composites exhibited higher tensile strength (33.9 MPa) and significantly greater ductility. Charpy impact tests showed that PLA/RDF composites exhibited a higher average impact energy (0.8513 J) than PP/RDF composites (0.7032 J). Moisture absorption tests demonstrated that both composite systems exhibited significant hydrophilic behavior, with a mass increase of approximately 12%–15% after 3 weeks. These findings highlight the potential of reused post-consumer denim fabric as a sustainable reinforcement material for the development of scalable thermoplastic composite structures with enhanced mechanical performance and environmental durability.