Policy PointsThe erosion of electoral democracy in the United States in recent decades may have contributed to the high and rising working‐age mortality rates, which predate the COVID‐19 pandemic.Eroding electoral democracy in a US state was associated with higher working‐age mortality from homicide, suicide, and especially from drug poisoning and infectious disease.State and federal efforts to strengthen electoral democracy, such as banning partisan gerrymandering, improving voter enfranchisement, and reforming campaign finance laws, could potentially avert thousands of deaths each year among working‐age adults. Context: Working‐age mortality rates are high and rising in the United States, an alarming fact that predates the COVID‐19 pandemic. Although several reasons for the high and rising rates have been hypothesized, the potential role of democratic erosion has been overlooked. This study examined the association between electoral democracy and working‐age mortality and assessed how economic, behavioral, and social factors may have contributed to it. Methods: We used the State Democracy Index (SDI), an annual summary of each state's electoral democracy from 2000 to 2018. We merged the SDI with annual age‐adjusted mortality rates for adults 25–64 years in each state. Models estimated the association between the SDI and working‐age mortality (from all causes and six specific causes) within states, adjusting for political party control, safety net generosity, union coverage, immigrant population, and stable characteristics of states. We assessed whether economic (income, unemployment), behavioral (alcohol consumption, sleep), and social (marriage, violent crime, incarceration) factors accounted for the association. Findings: Increasing electoral democracy in a state from a moderate level (defined as the third quintile of the SDI distribution) to a high level (defined as the fifth quintile) was associated with an estimated 3.2% and 2.7% lower mortality rate among working‐age men and women, respectively, over the next year. Increasing electoral democracy in all states from the third to the fifth quintile of the SDI distribution may have resulted in 20,408 fewer working‐age deaths in 2019. The democracy–mortality association mainly reflected social factors and, to a lesser extent, health behaviors. Increasing electoral democracy in a state was mostly strongly associated with lower mortality from drug poisoning and infectious diseases, followed by reductions in homicide and suicide. Conclusions: Erosion of electoral democracy is a threat to population health. This study adds to growing evidence that electoral democracy and population health are inextricably linked. [ABSTRACT FROM AUTHOR]