The transition to parenthood can be a challenging time for the relationships of new parents and result in declines in relationship satisfaction. Although a robust literature has identified characteristics that predict changes in relationship satisfaction during this period, the relationships of Black mothers postpartum remain understudied. To address this gap, we examined a set of relational, individual, and external characteristics as predictors of relationship satisfaction trajectories over the first four months postpartum. First‐time Black mothers (N = 93, 22.6% married, 52.7% cohabiting, 24.7% not cohabiting) reported on relational, individual, and external characteristics at 1 week postpartum and their relationship satisfaction at 1, 8, and 16 weeks postpartum. Mothers who reported more commitment and partner support were higher in initial satisfaction, as were mothers who were married or cohabiting with a partner (relative to mothers who were not cohabiting with their partner). Mothers with clinically significant depressive symptoms at 1 week postpartum had lower initial relationship satisfaction than mothers without clinically significant depressive symptoms. Mothers' sleep difficulties and experiences of racial discrimination were associated with changes in relationship satisfaction over time; mothers experiencing more sleep difficulties and racial discrimination experienced larger declines in satisfaction. These findings offer new insights into risk and protective factors associated with relationship satisfaction among Black mothers during the early postpartum period and can inform multicomponent interventions to enhance their relationship functioning.