Research has established breastfeeding as protective of maternal health, but little is known about the ways breastfeeding interacts with chronic stress pathways and interfaces with stressors such as discrimination and neighborhood deprivation, which are salient in the experiences of many marginalized communities. This research addresses these knowledge gaps through secondary analyses of prospective cohort data generated by the Community Child Health Research Network through Community Based Participatory Research processes. Analytical samples were derived from 2510 postpartum women from five regions in the U.S. who self-identified as Black, Hispanic, or White. Study 1 investigated and found an inverse association between breastfeeding duration and postpartum allostatic load, a multisystem biomarker of chronic stress. Mothers who breastfed ≥ 6 months had significantly lower allostatic load at six (β: -0.41; 95% CI: -0.71, -0.11) and twelve months postpartum (β: -0.36; 95% CI: -0.69, -0.036), compared to mothers who never breastfed, while controlling for confounders. Study 2 applied the positive deviance approach to explore characteristics of resiliency that enabled mothers to breastfeed for ≥ 3 months despite risk exposure. Positive deviant mothers were more likely to believe that breastfeeding is the best method of feeding and were more likely to receive positive breastfeeding influence from family, friends, and healthcare providers. Optimism, community cohesion, spirituality, history of breastfeeding another child, and family history of breastfeeding were also important contributors to resiliency. Study 3 tested and affirmed hospital use of formula as a mediator on the causal pathway of the inverse association between neighborhood deprivation and breastfeeding duration. When modeling with a deprivation index characterizing neighborhoods with a high proportion of Black residents, neighborhood deprivation was positively associated with hospital formula use, which in turn reduced breastfeeding duration. Mothers were predicted to breastfeed for 5.02 weeks when categorized as living in the most deprived neighborhoods compared to 13.74 weeks in the least deprived neighborhoods. This research offers novel understandings of breastfeeding’s potential to attenuate chronic stress, highlights the resiliency of mothers, and underscores the pervasiveness of racism and its negative impact on breastfeeding.