Maternal depression is associated with instability within the family environment and increases in offspring substance use across adolescence. Rates of delay discounting, or the tendency to select smaller rewards that are immediately available relative to larger, but delayed rewards, are also associated with steeper increases in substance use among youth. Moreover, recent research suggests that early unstable environments may reinforce youths’ propensity towards opportunistic decision making and delay discounting specifically. The current prospective, longitudinal study examined links between maternal depressive symptoms, adolescent delay discounting, and subsequent substance use. Participants included 247 adolescents and their mothers who were assessed annually over a 6-year period (from ages 13 to 19 years). Results supported a small but significant mediation effect. Specifically, maternal depressive symptoms predicted increases in adolescent delay discounting, which, in turn, predicted steeper increases in adolescent substance use over time. Thus, youth decision making may represent a mechanism linking maternal depression and adolescent risk behaviors. Findings indicate the potential for interventions targeting parental psychopathology to prevent subsequent adolescent substance use.