Background Research has suggested optimism is associated with healthy aging and exceptional longevity, but most studies were conducted among non‐Hispanic White populations. We examined associations of optimism to longevity across racial and ethnic groups and assessed healthy lifestyle as a possible mediating pathway. Methods Participants from the Women's Health Initiative (N = 159,255) completed a validated measure of optimism and provided other demographic and health data at baseline. We evaluated associations of optimism with increments in lifespan using accelerated failure time models, and with likelihood of exceptional longevity (survival to age ≥90) using Poisson regression models. Causal mediation analysis explored whether lifestyle‐related factors mediated optimism‐lifespan associations. Results After covariate adjustment, the highest versus lowest optimism quartile was associated with 5.4% (95% confidence interval CI = 4.5, 6.4%) longer lifespan. Within racial and ethnic subgroups, these estimates were 5.1% (95%CI = 4.0, 6.1%) in non‐Hispanic White, 7.6% (95%CI = 3.6, 11.7%) in Black, 5.4% (95%CI = −0.1, 11.2%) in Hispanic/Latina, and 1.5% (95% CI = −5.0, 8.5) in Asian women. A high proportion (53%) of the women achieved exceptional longevity. Participants in the highest versus lowest optimism quartile had greater likelihood of achieving exceptional longevity (e.g., full sample risk ratio = 1.1, 95%CI = 1.1, 1.1). Lifestyle mediated 24% of the optimism‐lifespan association in the full sample, 25% in non‐Hispanic White, 10% in Black, 24% in Hispanic/Latina, and 43% in Asian women. Conclusions Higher optimism was associated with longer lifespan and a greater likelihood of achieving exceptional longevity overall and across racial and ethnic groups. The contribution of lifestyle to these associations was modest. Optimism may promote health and longevity in diverse racial and ethnic groups. Future research should investigate these associations in less long‐lived populations. See related Editorial by Cobert et al. and article by Jeffrey M. Levine in this issue.