Saint Martin’s island, located at the southernmost tip of Bangladesh, has significant ecological value for being most favourite tourist spot and acting as a nesting site for many internationally vulnerable marine species. This island’s marine biodiversity is exceptionally wealthy due to its favorable environment, but its marine environment is facing threats day by day due to natural calamities, various types of pollution, and other anthropogenic activities. This study was conducted on Saint Martin’s Island, through assessing the quality of seawater collected from 9 stations, determined using the Global Positioning System. Various physicochemical properties: pH, conductivity, total dissolved solids, turbidity, salinity, density, viscosity, refractive index and dissolved oxygen with concentration of phosphate and nitrate were measured. Concentration of arsenic, lead, mercury, zinc, sodium and magnesium were also investigated by Atomic Absorption Spectrophotometer and the trend of average concentration of mineral and heavy metals was Na > Mg and Zn > Pb > Hg > As, respectively. Furthermore, several water quality indices were calculated for physicochemical parameters and concentration of heavy metals where category of seawater quality was found “Good” according to Canadian Council of Ministers of Environment (CCME) Water Quality Index (WQI) and Weighted Arithmetic (WA) Water Quality Index (WQI) revealed “poor” quality. Thus, seawater quality parameters have been critically analysed, correlated and essential findings were noted and. Obtained results highlight variation in most of the seawater quality parameters of Saint Martin and have a good correlation with each other.