Microplastics (MPs) are prevalent in coastal habitats, but their occurrence in highly vulnerable coastal zones and human exposure risk are poorly understood, especially in developing nations like Bangladesh. This inquiry focused on the prevalence and potential hazards of MPs in surface sediment and shallow groundwater samples collected from 12 sites in Cox’s Bazar, Bangladesh, from August to October 2023. Using stereomicroscopy and FTIR, MPs were quantified, with concentrations ranging from 60 to 813.33 MPs/kg in surficial sediment and 3.34 to 36.66 MPs/L in shallow groundwater, with mean values of 294.38 ± 26.61 MPs/kg and 18.91 ± 4.75 MPs/L. The dominant MPs were composed of transparent and white fibers, ranging in size from 0 to 0.5 mm, with HDPE (High-Density Polyethylene) and PP (Polypropylene) identified as the most commonly found polymers. To assess MP exposure in humans and the environment, this investigation used three indices: the polymer hazard index (PHI), the pollutant load index (PLI), and the estimated daily intake (EDI). The findings indicate that children exhibit greater exposure than adults, with observed low contamination levels, alongside a spectrum of toxicity from moderate to extreme. This study enhances understanding of MP contamination in the surficial sediments and shallow groundwater of Bangladesh, highlighting the need for further investigation into ecotoxicology, human health risks, legislation, and related issues.