Background Many U.S. women fall short of meeting the recommendations on breastfeeding. While prenatal demographic factors have been well researched in relation to breastfeeding, psychosocial maternal characteristics are less understood but could be important predictors of breastfeeding initiation and duration. Objectives This study examined primiparous maternal psychosocial characteristics and temperamentally-based negative infant affect as predictors of breastfeeding initiation and duration while accounting for depression and sociodemographic covariates. Methods Prenatally, 237 primiparous women were administered the Adult Attachment Interview and completed a measure of beliefs related to infant crying. At six months post-partum negative infant affect was assessed via mother report. Breastfeeding was assessed at six months and one year postpartum via mother report. Results Results indicated that younger, low income, less educated, single, ethnic minority mothers and mothers with elevated depressive symptoms were less likely to initiate breastfeeding and breastfed for a shorter period than other women. Women who initiated breastfeeding tended to have higher adult attachment coherence scores (more secure attachment) than those who did not initiate breastfeeding (Median score of 6.00 vs. 4.00). An interaction was observed between negative infant affect and beliefs about crying related to spoiling, such that earlier cessation of breastfeeding was observed among mothers who reported high levels of negative infant affect and strongly endorsed the belief that responding to cries spoils infants, (Hazard Ratio = 1.71, p < .01). Conclusions Although these psychosocial variables predicted relatively little variation in breastfeeding over and above covariates, the results suggest some novel approaches to promote breastfeeding.