Importance In 2011, critical congenital heart disease was added to the US Recommended Uniform Screening Panel for newborns, but whether state implementation of screening policies has been associated with infant death rates is unknown. Objective To assess whether there was an association between implementation of state newborn screening policies for critical congenital heart disease and infant death rates. Design, Setting, and Participants Observational study with group-level analyses. A difference-in-differences analysis was conducted using the National Center for Health Statistics’ period linked birth/infant death data set files for 2007-2013 for 26 546 503 US births through June 30, 2013, aggregated by month and state of birth. Exposures State policies were classified as mandatory or nonmandatory (including voluntary policies and mandates that were not yet implemented). As of June 1, 2013, 8 states had implemented mandatory screening policies, 5 states had voluntary screening policies, and 9 states had adopted but not yet implemented mandates. Main Outcomes and Measures Numbers of early infant deaths (between 24 hours and 6 months of age) coded for critical congenital heart disease or other/unspecified congenital cardiac causes for each state-month birth cohort. Results Between 2007 and 2013, there were 2734 deaths due to critical congenital heart disease and 3967 deaths due to other/unspecified causes. Critical congenital heart disease death rates in states with mandatory screening policies were 8.0 (95% CI, 5.4-10.6) per 100 000 births (n = 37) in 2007 and 6.4 (95% CI, 2.9-9.9) per 100 000 births (n = 13) in 2013 (for births by the end of June); for other/unspecified cardiac causes, death rates were 11.7 (95% CI, 8.6-14.8) per 100 000 births in 2007 (n = 54) and 10.3 (95% CI, 5.9-14.8) per 100 000 births (n = 21) in 2013. Early infant deaths from critical congenital heart disease through December 31, 2013, decreased by 33.4% (95% CI, 10.6%-50.3%), with an absolute decline of 3.9 (95% CI, 3.6-4.1) deaths per 100 000 births after states implemented mandatory screening compared with prior periods and states without screening policies. Early infant deaths from other/unspecified cardiac causes declined by 21.4% (95% CI, 6.9%-33.7%), with an absolute decline of 3.5 (95% CI, 3.2-3.8) deaths per 100 000 births. No significant decrease was associated with nonmandatory screening policies. Conclusions and Relevance Statewide implementation of mandatory policies for newborn screening for critical congenital heart disease was associated with a significant decrease in infant cardiac deaths between 2007 and 2013 compared with states without these policies.