Globally, radioactivity in marine sediments results from naturally occurring radioactive materials and artificial radionuclides. This has been described as a severe environmental concern impacting human health and marine ecosystems. This study investigates and presents the global distribution and levels of radioactivity in coastal sediments, focusing on Durban beaches (Umhlanga Rocks Beach, Addington Beach, Ushaka Beach, and Bay of Plenty Beach), South Africa, as a case study. A thallium-doped gamma-ray spectrometry detector was used to measure the radioactivity concentration in the marine sediments along the Durban beaches of South Africa. Most reported values globally were classified as low-radiation areas across marine environments. Additionally, the overall mean activity concentrations of 226Ra, 232Th, and 40 K in the marine sediment samples from South Africa were 124.82 ± 0.76, 53.91 ± 0.26, and 359.35 ± 2.59 Bq.kg−1, respectively. The reported values for the case study area were compared with those from other parts of the globe and with the permissible global averages of 32, 45, and 412 Bq.kg−1 for 226Ra, 232Th, and 40K, respectively. This study advances our knowledge of radioactivity dispersion in marine ecosystems and guides environmentally friendly and sustainable coastal management practices by fusing global perspectives with specific case studies.