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The accumulation of marine debris along coastal sites is a global issue, yet there is limited knowledge about this problem, particularly in island nations. In this context, the present study focused on assessing the abundance and composition of marine macro debris (>2.5 cm) as well as the abundance and characteristics of plastics along the eight beaches of the western coast of Sri Lanka. Among the macro debris, we found that local-origin, end-consumer products and packaging materials were dominant. Plastic waste was the most abundant macro debris (>50 % of debris) in all sites. Size classification of plastic waste indicated the presence of macro- (>2.5 cm), meso (5 mm–2.5 cm) and microplastics (<5 mm) in all sites where they had spatial differences in abundance. The average macroplastic abundance along the western coast of Sri Lanka was 28.51 particles/100 m². The average meso- and microplastic abundances in this study were 19.83 ± 1.56 and 51.41 ± 1.62 particles/m², respectively. Improper disposal of plastic waste, the MV X-Press Pearl ship accident, proximity to the river mouth, surface ocean currents and wind patterns likely contributed to the spatial variation of marine macro debris and plastic pollution along the western coast of Sri Lanka. Among the studied sites, there was a significant positive correlation (p < 0.05) among the macro-, meso-, and microplastic abundance. This indicates macro-and mesoplastic abundance can be utilized as a proxy for the microplastic abundance along the western coast of Sri Lanka. Macroplastic pollution status calculated by the clean coast index (CCI) classified Crow Island as 'extremely dirty' (CCI>20). Our study highlights the importance of implementing effective waste management systems and raising public awareness on proper waste disposal to manage marine debris pollution along the western coast of Sri Lanka.