Inequitable gender norms can contribute to rapid repeat pregnancies and adverse maternal health outcomes among adolescent girls and young women. This study examined associations between male partners’ gender-equitable attitudes and behaviors and postpartum family planning (FP) and maternal and newborn health (MNH) outcomes among first-time mothers aged 15–24 in Kinshasa, Democratic Republic of the Congo. Participants were 1335 couples who were successfully interviewed in the Momentum project’s 2018 baseline and 2020 endline surveys. Multivariable regression models were used to analyze predictors of postpartum FP discussion and use, shared MNH decision making, completion of the maternal health continuum of care, and exclusive breastfeeding. Male involvement in maternal health was significantly associated with FP discussion and shared decision making. Male partners’ willingness to be involved in routine childcare and shared decision making were significant positive predictors of exclusive breastfeeding. Postpartum FP outcomes were shaped by the intersection of marital status and male partners’ gender-equitable attitudes, intimate partner violence perpetration, and willingness to engage in routine childcare activities to constitute advantage for some outcomes and disadvantage for others. Interventions must use multiple measures to better understand how young mothers’ health outcomes are shaped by their male partners’ gender-related attitudes and behaviors.