Microplastics (MPs) and nanoplastics (NPs) infiltrate every environmental matrix, presenting increasing risks to ecological stability and human well-being. This review compiles worldwide data from 228 studies to examine trends specific to polymers, shape, source of origin, transport mechanisms, and the emerging risks of MPs/NPs across marine, freshwater, groundwater, terrestrial, and atmospheric environments. Polyethylene (PE) and polypropylene (PP) are the leading fibrous contaminants in freshwater systems, soil, and aquifers, mainly due to packaging, textiles, and wastewater discharges. Marine ecosystems gather fragment-shaped PE and PP from coastal waste breakdown and fishing practices, whereas atmospheric MPs/NPs—mainly polyethylene terephthalate (PET), polyamide (PA), and polyvinyl chloride (PVC) fibers—arise from synthetic fabrics and urban pollutants. The research demonstrates how the shapes of particles and polymer composition influence the environmental behaviour of various pollutants in diverse settings. Emerging threats involve MPs/NPs acting as carriers for pathogens (e.g., SARS-CoV-2), interfering with ocean carbon sequestration through “plastic snow,” and hastening sea-ice melting by reducing albedo. Climate interactions are bidirectional—rising temperatures accelerate plastic fragmentation, while MPs alter greenhouse gas fluxes by modifying soil microbial activity. Analytical progress (FTIR, Raman spectroscopy) predominates polymer characterization, but there are still gaps in identifying NPs and measuring long-term ecotoxicological effects. The study also highlights how ocean currents, atmospheric movements, and water cycle mechanisms contribute to the movement of plastics to remote areas, such as Arctic ice and underground water sources. Although studies on MPs and NPs are increasing, notable gaps remain in comprehending their lasting effects and properties across various environmental matrices. This research establishes a framework for prioritizing interventions to combat the plastic pollution crisis by connecting source-to-sink pathways and cross-matrix interactions.