Air pollution presents a significant challenge in Bangladesh, particularly in its capital, Dhaka, which ranks among the world's least livable cities. The prevalence of PM_2.5, a prominent air pollutant, has dire health consequences for the nation's residents. This study investigated the intricate relationship between elevated levels of PM_2.5 and mortality rates linked to diseases such as Ischemic Heart Disease (IHD), Chronic Obstructive Pulmonary Disease (COPD), Cerebrovascular Disease (CVD), Lower Respiratory Infections (LRI), and Lung Cancer (LC). This study utilized station data (2012-2022) and gridded data (2000-2021) for PM_2.5, gridded population data (2000-2022) and cause-specific base mortality rate of 2019 for Bangladesh. It explored the diurnal, seasonal, and annual variability of PM_2.5 concentrations throughout the country. Relative risk and disease-specific mortality rates were estimated using the Integrated Exposure-Response (IER) and Global Exposure Mortality Model (GEMM). The results revealed large disparities in disease burden among geographic regions and timeframes. PM_2.5 levels were generally low in the early morning and high in the late afternoon in all cities, except for some locations in Dhaka, where they were high at night. Seasonal variability revealed that pollution in winter was more than three times higher than in the monsoon season. Air pollution in Dhaka remained higher than WHO standard limits in almost all seasons, except for a few hours during peak monsoons. Very few stations in the country exhibited less than 5 μg/m³ of PM_2.5 at the 24-hour level. Higher PM_2.5 concentrations, especially in major cities, were linked to increased excess mortality rates for the mentioned diseases. This study can enhance our comprehension of the public health consequences of ambient air pollution in Bangladesh, which necessitates further extensive exploration.