Background: Particulate air pollution causes a spectrum of adverse health effects affecting the respiratory, cardiovascular, neurological, and metabolic systems that are hypothesised to be driven by inflammation and oxidative stress. Millions of premature deaths each year are attributed to exposure to ambient particulate matter (PM). We quantified health and economic impacts from long-term exposure to ambient PM2.5 in the population of Thailand for 2016. Methods: We collected data on ambient PM2.5 concentrations from automatic monitoring stations across Thailand over 1996 to 2016. We used historic exposure to PM2.5 to estimate the mortality in each province from lower respiratory infections (LRI), stroke, chronic obstructive pulmonary disease (COPD), lung cancer, and ischaemic heart disease (IHD), and also assessed diabetes mortality, as well as incident cases of dementia and Parkinson's disease, in supplementary analyses. We applied risk estimates from the Global Exposure Mortality Model (GEMM) to calculate attributable mortality and quantify Disability-Adjusted Life Years (DALYs); we based economic costs on the Value of a Statistical Life (VSL). Results: We calculated 50,019 (95% Confidence Interval [CI]: 33,169 to 63,596) deaths and 508,918 (95% CI: 349,983 to 639,264) DALYs in 2016 attributed to long-term PM2.5 exposure in Thailand. Population Attributable Fractions (PAFs) ranged from 20% (95% CI: 10% to 29%) for stroke to 48% (95% CI: 27% to 63%) for LRIs. Based on the VSL, we calculated a cost of US$ 60.9 billion (95% CI: US$ 40.3 to 77.3 billion), which represents nearly 15% of Thailand's GDP in 2016. Conclusion: While progress has been made to reduce exposure to ambient PM2.5 in Thailand, continued reductions based on stricter regulatory limits for PM2.5 and other air pollutants would help prolong life, and delay, or prevent, onset of cardiorespiratory and other diseases.