Background: Supplementation in the newborn nursery has been associated with shorter breastfeeding duration. However, supplementation may at times be necessary. Research Aim: To determine the association between type of supplementation in the newborn nursery (mother’s own milk, formula, donor human milk) and breastfeeding outcomes at 2 and 6 months of age. Methods: This was a prospective, longitudinal, observational multi-group cohort study. In total, 2,343 surveys were sent to parents who, prior to delivery, indicated intent to exclusively breastfeed. Participants were grouped by type of nursery supplementation. Surveys asked about breastfeeding outcomes when infants were 2 and 6 months old. Our final analytic sample included data from 1,111 healthy newborns ≥ 35 weeks. We used multiple logistic regression to compare future breastfeeding outcomes for infants who were exclusively directly breastfed or who received supplementation during their birth hospitalization. Results: Both the donor human milk and formula groups had decreased breastfeeding at 2 and 6 months compared to the exclusively directly breastfed group. Notably, for infants who received formula compared to donor human milk, the odds of breastfeeding at 2 and 6 months were 74% and 58% lower, respectively ( OR = 0.26, 95% CI [0.12, 0.56] at 2 months; OR = 0.42, 95% CI [0.19, 0.94] at 6 months). The donor human milk group had lower odds of breastfeeding at both follow up times compared to the mother’s own milk group. Conclusion: Among those who intend to breastfeed, supplementation with donor human milk instead of formula in the newborn nursery may support longer breastfeeding.