Background <p>As mortality from ambient PM_2.5 pollution rises and the role of greenspaces in sustainable development grows, understanding relevant national trends and their associations becomes critical. This study aimed to describe the spatiotemporal trends in greenspace access and age-standardized mortality rates (ASMR) attributable to ambient PM_2.5, and to explore their association.</p> Methods <p>Data on ASMR attributable to ambient PM_2.5 from 2000 to 2020 across 204 countries and territories were obtained from Global Burden of Disease Study (GBD) 2021. ‌Greenspace access metrics were derived from the Global Land Analysis and Discovery dataset and linked to the GBD database through standardized country/territory names and temporal alignment. The estimated annual percentage change (EAPC) was calculated to analyze secular trends in the two data sources and the Gini index was used to assess inequalities in greenspace access.</p> Results <p>Globally, all-cause ASMR per 100,000 inhabitants attributable to ambient PM_2.5 decreased from 63.5 in 2000 to 55.4 in 2020 and greenspace access levels decreased from 37.0% in 2000 to 28.6% in 2020. ASMR attributable to ambient PM_2.5 was higher in children under 5 years and 60-years-and-older age groups, and North Africa and Middle East were the high-risk areas. Greenspace access levels decreased in all GBD regions except for Oceania (EAPC = 0.18, 95% CI: 0.16 to 0.20). Inequality in greenspace increased by nearly one-fifth in 2020 (Gini: 0.24) compared to 2000 (Gini: 0.20) in countries with a low sociodemographic index. A negative association was observed between greenspace access and PM_2.5-related mortality for ischemic heart disease, stroke, chronic obstructive pulmonary disease, and neonatal disorders.</p> Conclusions <p>Our findings highlight the importance of prioritizing equity-focused green policies to reduce mortality risk associated with ambient PM_2.5.</p>