Background: Research shows that individuals can improve mental health by increasing experiences of positive emotions. However, the role of positive emotions in perinatal mental health has not been investigated. This study explored the extent to which positive emotions during infant feeding are associated with maternal depression and anxiety during the first year postpartum. Materials and Methods: One hundred and sixty-four women drawn from a longitudinal cohort of mother-infant dyads were followed from the third trimester through 12 months postpartum. We measured positive emotions during infant feeding at 2 months using the mean subscale score of the modified Differential Emotions Scale. Depression and anxiety symptoms were assessed with the Beck Depression Inventory-II and State Trait Anxiety Inventory-State subscale at months 2, 6, and 12. Generalized linear mixed models were used to estimate crude and multivariable associations. Results: Among women with no clinical depression during pregnancy, higher positive emotions during infant feeding at 2 months were associated with significantly fewer depression symptoms at 2, 6, and 12 months and with lower odds of clinically significant depression symptoms at 2 and 6 months. In contrast to depression outcomes, women with clinical anxiety during pregnancy who experienced higher positive emotions had significantly fewer anxiety symptoms at 2, 6, and 12 months and lower odds of clinically significant anxiety at 2 and 6 months. Conclusions: Positive emotions during infant feeding are associated with depression and anxiety outcomes during the first year postpartum and may be a modifiable protective factor for maternal mental health.