Polyolefins account for more than half of global plastic production. However, their short service life and limited recyclability have led to severe environmental pollution and substantial resource loss. Catalytic valorization has emerged as a promising strategy to convert polyolefin waste into high-value chemicals and fuels. In practice, progress toward deployable valorization technologies depends on coordinated innovation across the connected catalyst–process–reactor chain at different length scales, spanning molecular-scale active-site chemistry, process development and optimization, and reactor selection and design. This review describes recent advances in the catalytic valorization of polyolefins from an integrated, multiscale perspective, encompassing catalyst design, process engineering, and reactor development. We first discuss the design principles and reaction mechanisms of representative catalytic systems, including metal catalysts, solid acid catalysts, bifunctional catalysts, and ionic liquid catalysts, with an emphasis on how catalyst properties dictate reaction pathways and product selectivity. Building on these insights, process innovations, such as mixed catalysts, co-conversion with small molecules (CH4, CO2, C2H4, CO, and CH3OH), and external-field-assisted transformations (plasma, microwave, and Joule heating), are analyzed in terms of their roles in enhancing catalytic activity, selectivity, and stability. Furthermore, recent developments in batch, fixed-bed, and fluidized-bed reactors are reviewed, highlighting the influence of heat and mass transfer, continuous operation, and scalability on overall process performance. Finally, we conclude by outlining critical gaps that currently hinder translation from lab studies to real-world waste streams and by proposing opportunities to accelerate catalyst and process development.