BACKGROUND: The postpartum period is associated with a high risk of illness episodes in women with bipolar disorder (BD) and is a critical developmental phase for both a new mother and her infant. This mixed-methods study aimed to investigate the occurrence of mood symptoms among infant mothers with BD in the first year postpartum, as well as their perceptions of the first year, their challenges and their strategies for wellbeing. METHODS: Twenty-six women with BD participated. Mood symptoms were assessed at 3 and 12 months postpartum with the Inventory of Depressive Symptomatology and Young Mania Rating Scale. Occurrences of additional postpartum mood deviations were investigated through an interview at 12 months, which also covered the women's postpartum experiences. Thematic analysis was applied to the qualitative dataset (interviews and field notes). RESULTS: 42% of the women were euthymic or had only mild mood symptoms at 3 and 12 months. 58% had moderate to severe symptoms at either or both time points. A positive (38%) vs. mixed (62%) perception of the first year was strongly associated with euthymia-mild vs. moderate-severe mood deviations, as was the experience of maternal developmental achievement vs. struggles. The women experienced postpartum mood deviations and illness episodes as being particularly poorly timed. Further challenges included balancing self-care and infant mothering, familial relations, and negative experiences with the health and care systems. Illness acceptance with mindfulness of one's own and the infant's needs was a primary strategy for wellbeing, which was complemented by the support of one's partner and family and postpartum treatment. CONCLUSIONS: Our findings propose that without impeding mood deviations and concomitant challenges, infant mothers with BD can enjoy their new motherhood and experience phase-specific growth equally to healthy mothers. On the other hand, moderate to severe mood deviations can adversely impact the experience of the postpartum year and one's own sense of mothering. Efforts to prevent postpartum mood deviations need to be complemented with interventions that target phase-specific BD challenges and support wellbeing strategies for both the mother and her infant. In summary, women's needs to function as infant mothers must be considered in the postpartum treatment of BD.