Objectives Young parents may be particularly vulnerable to poor mental health during the postpartum period. Little research exists, however, to adequately describe trajectories of depressive symptoms during their transition to parenthood, particularly among young fathers. Therefore, we aim to explore trajectories of depressive symptoms from pregnancy through 1 year postpartum among young expectant mothers and their partners. Methods Data are derived from a longitudinal cohort of pregnant adolescent females (ages 14-21; n = 220) and their male partners (n = 190). Multilevel regression models examined the impact of time on depressive symptoms, and generalized linear regression models examined predictors of experiencing elevated depressive symptoms. Results Depressive symptoms significantly decreased from pregnancy through 1 year postpartum among young females. Overall, depressive symptoms did not significantly change over time among young males. Predictors of elevated depressive symptoms common across genders included social support and relationship satisfaction. Marijuana use resulted in almost twice the odds of experiencing elevated depressive symptoms among young fathers (OR 1.82; 95 % CI 1.04, 3.20). Conclusion for Practice Providing strategies for strengthening social support networks among young parents may be an effective way to improve mental health among young parents, particularly during this period of potential social isolation. Additionally, providing tools to strengthen relationships between partners may also be effective for both young mothers and fathers. Substance use may be a marker for depressive symptoms among young fathers and thus screening for substance use could be important to improving their mental health. Future research is needed to better understand how IPV affects mental health, particularly among young fathers.