Background Few studies have investigated the longitudinal association between breastfeeding and maternal cardiovascular disease ( CVD ) outcomes. This study examined the association between breastfeeding and CVD hospitalization and mortality in a large Australian cohort. Methods and Results Baseline questionnaire data (2006–2009) from a sample of 100 864 parous women aged ≥45 years from New South Wales, Australia, were linked to hospitalization and death data until June 2014 and December 2013, respectively. Analysis was restricted to women without self‐reported medically diagnosed CVD at baseline or without past CVD hospitalization 6 years before study entry. Never versus ever breastfeeding and average breastfeeding duration per child, derived from self‐reported lifetime breastfeeding duration and number of children, and categorized as never breastfed, <6, >6 to 12, or >12 months/child, were assessed. Cox proportional hazards models were used to explore the association between breastfeeding and CVD outcomes. Covariates included sociodemographic characteristics, lifestyle risk factors, and medical and reproductive history. There were 3428 (3.4%) first CVD ‐related hospital admissions and 418 (0.4%) deaths during a mean follow‐up time of 6.1 years for CVD hospitalization and 5.7 years for CVD mortality. Ever breastfeeding was associated with lower risk of CVD hospitalization (adjusted hazard ratio [95% CI]: 0.86 [0.78, 0.96]; P =0.005) and CVD mortality (adjusted hazard ratio [95% CI]: 0.66 [0.49, 0.89]; P =0.006) compared with never breastfeeding. Breastfeeding ≤12 months/child was significantly associated with lower risk of CVD hospitalization. Conclusions Breastfeeding is associated with lower maternal risk of CVD hospitalization and mortality in middle‐aged and older Australian women. Breastfeeding may offer long‐term maternal cardiovascular health benefits.