This study assessed the activity concentrations of gross α, gross β, and primordial radionuclides (238U, 232Th, and 40K) in 21 surface sediment samples collected from the North Chennai to Pondicherry coastal area, India. An alpha radiation counting system with a ZnS(Ag) detector, a low-background beta counter, and a NaI(Tl) γ-ray detector were used for the measurements. The average activity concentration of gross α and β were 32.39 Bq kg−1 and 621.26 Bq kg−1, respectively. The average activities of 238U (60 Bq kg−1), 232Th (70 Bq kg−1), and 40K (573 Bq kg−1) exceeded the world average values reported by UNSCEAR. The average gamma absorbed dose rate (178 nGy h−1) and excess lifetime cancer risk (0.77 × 10−3 mSv y−1) were above recommended safety levels. In addition, the presence of radioactive minerals such as monazite, zircon, and rutile were confirmed by using the X-ray diffraction technique. The statistical analyses, including Pearson correlation, and cluster analysis were performed to explore the association between radiological variables. The findings indicate elevated levels of natural radioactivity in the study area, suggesting the need for regulatory control over the use of sediments to mitigate potential health risks.