BackgroundThere is growing evidence that sleep duration and quality may be associated with cardiovascular harm and mortality.Methods and ResultsWe conducted a systematic review, meta‐analysis, and spline analysis of prospective cohort studies that evaluate the association between sleep duration and quality and cardiovascular outcomes. We searched MEDLINE and EMBASE for these studies and extracted data from identified studies. We utilized linear and nonlinear dose‐response meta‐analysis models and used DerSimonian–Laird random‐effects meta‐analysis models of risk ratios, with inverse variance weighting, and the I2 statistic to quantify heterogeneity. Seventy‐four studies including 3 340 684 participants with 242 240 deaths among 2 564 029 participants who reported death events were reviewed. Findings were broadly similar across both linear and nonlinear dose‐response models in 30 studies with >1 000 000 participants, and we report results from the linear model. Self‐reported duration of sleep >8 hours was associated with a moderate increased risk of all‐cause mortality, with risk ratio, 1.14 (1.05–1.25) for 9 hours, risk ratio, 1.30 (1.19–1.42) for 10 hours, and risk ratio, 1.47 (1.33–1.64) for 11 hours. No significant difference was identified for periods of self‐reported sleep <7 hours, whereas similar patterns were observed for stroke and cardiovascular disease mortality. Subjective poor sleep quality was associated with coronary heart disease (risk ratio, 1.44; 95% confidence interval, 1.09–1.90), but no difference in mortality and other outcomes.ConclusionsDivergence from the recommended 7 to 8 hours of sleep is associated with a higher risk of mortality and cardiovascular events. Longer duration of sleep may be more associated with adverse outcomes compared with shorter sleep durations.