The escalating global demand for sustainable energy and the environmental burden of organic and synthetic waste have intensified interest in co-pyrolysis, a thermochemical process that simultaneously converts biomass and various waste materials into valuable fuels and chemicals. This review presents an up-to-date, factorial analysis of co-pyrolysis systems, emphasizing synergistic interactions between lignocellulosic and non-lignocellulosic biomass, such as plastics, tires, sewage sludge, and other waste streams. The study systematically examines key factors such as feedstock properties, thermal decomposition mechanisms, and operational parameters (e.g., temperature, heating rate, residence time, particle size, and mixing ratio). It also highlights catalyst development, including zeolite- and biochar-based systems, to enhance product yield, aromatic selectivity, and hydrogen production while reducing oxygenated compounds. The review also discusses emerging trends in bio-oil upgrading techniques and advanced characterization protocols to address challenges in stability, acidity, and fuel applicability. We also review integrating co-pyrolysis with renewable technologies and artificial intelligence tools for predictive modeling, process optimization, and system scalability. Despite promising advances, critical gaps remain in mechanistic understanding, catalyst deactivation, long-term process viability, and comprehensive techno-economic and lifecycle assessments. This review offers actionable insights for researchers, engineers, and policymakers, providing a strategic roadmap to advance co-pyrolysis technologies toward industrial-scale implementation in a circular, low-carbon energy economy.